English how-to · updated 2026

Compound interest explained

The savings-and-loan search that shows up in every personal-finance class. This page has 100 important questions and answers. Original explainer for daily search — not a government login or live tracker.

Simple interest is earned only on the original principal. Compound interest is earned on the principal plus interest already added — interest on interest. The more often it compounds (yearly, monthly, daily), the faster a balance can grow — or a debt can swell.

Credit cards and some student loans compound. Savings accounts and index funds use the same maths in the other direction. The Rule of 72 is a rough “years to double” shortcut: 72 ÷ annual % rate.

100 important questions. Quick 10 is a random set; Full set plays every question.

100 questions and answers

Each item is a 4-option MCQ. Open a question, tap A–D. Green is correct, red is wrong. Original explainers — not copied match reports.

1. The official source for “compound interest” (learn desk, item 3) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

2. The official source for “compound interest” (learn desk, item 4) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

3. The official source for “compound interest” (learn desk, item 5) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

4. The official source for “compound interest” (learn desk, item 6) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

5. The official source for “compound interest” (learn desk, item 7) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

6. The official source for “compound interest” (learn desk, item 8) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

7. The official source for “compound interest” (learn desk, item 9) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

8. The official source for “compound interest” (learn desk, item 10) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

9. The official source for “compound interest” (learn desk, item 11) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

10. The official source for “compound interest” (learn desk, item 12) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

11. The official source for “compound interest” (learn desk, item 13) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

12. The official source for “compound interest” (learn desk, item 14) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

13. The official source for “compound interest” (learn desk, item 15) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

14. The official source for “compound interest” (learn desk, item 16) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

15. The official source for “compound interest” (learn desk, item 17) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

16. The official source for “compound interest” (learn desk, item 18) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

17. The official source for “compound interest” (learn desk, item 19) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

18. The official source for “compound interest” (learn desk, item 20) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

19. The official source for “compound interest” (learn desk, item 21) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

20. The official source for “compound interest” (learn desk, item 22) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

21. The official source for “compound interest” (learn desk, item 23) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

22. The official source for “compound interest” (learn desk, item 24) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

23. The official source for “compound interest” (learn desk, item 25) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

24. The official source for “compound interest” (learn desk, item 26) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

25. The official source for “compound interest” (learn desk, item 27) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

26. The official source for “compound interest” (learn desk, item 28) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

27. The official source for “compound interest” (learn desk, item 29) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

28. The official source for “compound interest” (learn desk, item 30) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

29. The official source for “compound interest” (learn desk, item 31) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

30. The official source for “compound interest” (learn desk, item 32) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

31. The official source for “compound interest” (learn desk, item 33) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

32. The official source for “compound interest” (learn desk, item 34) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

33. The official source for “compound interest” (learn desk, item 35) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

34. The official source for “compound interest” (learn desk, item 36) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

35. The official source for “compound interest” (learn desk, item 37) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

36. The official source for “compound interest” (learn desk, item 38) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

37. The official source for “compound interest” (learn desk, item 39) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

38. The official source for “compound interest” (learn desk, item 40) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

39. The official source for “compound interest” (learn desk, item 41) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

40. The official source for “compound interest” (learn desk, item 42) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

41. The official source for “compound interest” (learn desk, item 43) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

42. The official source for “compound interest” (learn desk, item 44) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

43. The official source for “compound interest” (learn desk, item 45) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

44. The official source for “compound interest” (learn desk, item 46) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

45. The official source for “compound interest” (learn desk, item 47) is

Tap A, B, C or D.

Answer: A) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

46. The official source for “compound interest” (learn desk, item 48) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

47. The official source for “compound interest” (learn desk, item 49) is

Tap A, B, C or D.

Answer: C) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

48. The official source for “compound interest” (learn desk, item 50) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

49. Compound interest is

Tap A, B, C or D.

Answer: D) interest on principal plus earlier interest

That is why time in the market matters.

50. Simple interest is calculated on

Tap A, B, C or D.

Answer: B) the original principal only

It grows in a straight line.

51. A = P(1 + r/n)^(nt) is

Tap A, B, C or D.

Answer: B) a standard compound-interest formula

P is principal, r is the annual rate.

52. The Rule of 72 says money at 8% doubles in about

Tap A, B, C or D.

Answer: A) 9 years

72 ÷ 8 = 9.

53. More frequent compounding, same APR, generally

Tap A, B, C or D.

Answer: B) grows a savings balance a bit faster

Read the APY, not only the APR.

54. Credit-card interest that compounds

Tap A, B, C or D.

Answer: A) can grow a unpaid balance quickly

Pay more than the minimum when you can.

55. Starting early helps because

Tap A, B, C or D.

Answer: A) time lets compounding work longer

Small regular amounts still add up.

56. Compound interest is not

Tap A, B, C or D.

Answer: C) the same as inflation, though both use percents

Inflation can eat real returns.

57. Principal means

Tap A, B, C or D.

Answer: A) the starting amount before interest is added

Interest is calculated on this, then on more if it compounds.

58. APR is the yearly rate stated; APY usually

Tap A, B, C or D.

Answer: D) includes the effect of compounding

Compare APY when shopping savings.

59. If interest compounds monthly rather than yearly, the same nominal rate

Tap A, B, C or D.

Answer: D) usually produces a slightly higher effective yield

Banks quote both figures for a reason.

60. A loan that compounds while you pay only a little

Tap A, B, C or D.

Answer: A) can see the balance stall or even grow

That is how card debt swells.

61. The Rule of 72 at 6% a year says doubling takes about

Tap A, B, C or D.

Answer: D) 12 years

72 divided by 6 is 12.

62. The Rule of 72 at 9% a year says doubling takes about

Tap A, B, C or D.

Answer: A) 8 years

72 divided by 9 is 8.

63. The Rule of 72 at 12% a year says doubling takes about

Tap A, B, C or D.

Answer: D) 6 years

It is a shortcut, not a bank contract.

64. Simple interest on 1000 at 10% for 3 years is

Tap A, B, C or D.

Answer: C) 300 of interest (100 a year)

Compound would add interest on the 100s too.

65. 1000 at 10% compounded yearly for 3 years becomes

Tap A, B, C or D.

Answer: B) 1331

1000 x 1.1 x 1.1 x 1.1 = 1331.

66. Effective annual rate (EAR) answers

Tap A, B, C or D.

Answer: A) what you actually earn or pay in a year after compounding

It lets you compare odd compounding schedules.

67. Continuous compounding is

Tap A, B, C or D.

Answer: A) the mathematical limit of compounding ever more often

The formula uses e to the power rt.

68. Inflation plus compound interest means

Tap A, B, C or D.

Answer: D) the real growth of savings can be much smaller than the nominal

A 5% APY with 5% inflation is about zero real.

69. Starting a regular transfer early helps because

Tap A, B, C or D.

Answer: C) more periods exist for interest to land on interest

Time is the hidden multiplier.

70. A higher rate for a short time can lose to

Tap A, B, C or D.

Answer: A) a modest rate left to compound for many years

Charts of long horizons make this obvious.

71. Compound frequency daily vs yearly, same APR, generally

Tap A, B, C or D.

Answer: A) daily wins by a small extra yield

Read the APY line.

72. Student loans that capitalise interest

Tap A, B, C or D.

Answer: B) add unpaid interest to the principal

Ask when capitalisation happens.

73. A sinking credit-card balance needs

Tap A, B, C or D.

Answer: A) payments above the interest being added

Minimums often barely cover interest.

74. Nominal rate without the compounding schedule is

Tap A, B, C or D.

Answer: A) incomplete for a fair comparison

Ask how often it compounds.

75. If you withdraw all interest each year, you have turned

Tap A, B, C or D.

Answer: C) compound interest back into simple on a flat principal

The pot stops growing by interest-on-interest.

76. Negative interest or large fees can

Tap A, B, C or D.

Answer: C) compound the wrong way and shrink a balance

Read the tariff.

77. A 72 / r shortcut fails badly when

Tap A, B, C or D.

Answer: C) rates are extreme or compounding is very frequent and you need precision

Use the real formula for contracts.

78. Present value is

Tap A, B, C or D.

Answer: A) today money equivalent of a future compounded sum

Discounting is compounding in reverse.

79. An annuity that compounds is

Tap A, B, C or D.

Answer: C) a stream of payments earning interest as they sit

Pensions and regular savers use this idea.

80. Doubling time shortens if you

Tap A, B, C or D.

Answer: D) raise the rate or compound more often

Or add fresh principal.

81. Credit cards often advertise a monthly rate that

Tap A, B, C or D.

Answer: B) compounds, so the yearly cost is higher than month x 12 in simple terms

The APR/EAR box is the honest comparison.

82. A savings APY of 4% does not

Tap A, B, C or D.

Answer: A) guarantee a 4% rise in real buying power

Inflation and tax sit in the middle.

83. Reinvested fund dividends are a form of

Tap A, B, C or D.

Answer: C) compounding if they buy more units

Spending the dividends stops that path.

84. The exponent nt in A = P(1+r/n)^(nt) is

Tap A, B, C or D.

Answer: D) how many compounding periods in t years

n is compounds per year; t is years.

85. If r is 0 in that formula, A equals

Tap A, B, C or D.

Answer: D) P

No rate, no growth from interest.

86. Compound interest on debt is why

Tap A, B, C or D.

Answer: D) waiting to repay can cost more than the original spend

Time works against the borrower.

87. A teaser rate that jumps later

Tap A, B, C or D.

Answer: C) can change the compounding path after the honeymoon

Read the revert rate.

88. Adding 100 a month is

Tap A, B, C or D.

Answer: D) new principal that will itself start compounding

Regular contributions dwarf a one-off for many people.

89. Comparing two pots, the winner is not always

Tap A, B, C or D.

Answer: D) the one with the prettier advertised headline rate

Fees compound too — against you.

90. A year of 10% then a year of 0% on the new balance

Tap A, B, C or D.

Answer: B) is not the same as 5% a year for two years

Order and compounding both matter.

91. Tax on interest each year can

Tap A, B, C or D.

Answer: C) slow compounding if you cannot shelter the account

Use legal wrappers if they exist where you live.

92. A balance that compounds quarterly four times at r/4

Tap A, B, C or D.

Answer: D) approximates the annual effective yield for that APR

That is what n = 4 means.

93. The opportunity cost of spending a windfall now is

Tap A, B, C or D.

Answer: C) the compounded sum you will not have later

That is why payday transfers help.

94. Compound growth assumes

Tap A, B, C or D.

Answer: A) you leave the interest invested (or unpaid, on a loan)

Withdrawals break the assumption.

95. A Rule of 70 or 69 is sometimes used because

Tap A, B, C or D.

Answer: D) it can fit continuous or frequent compounding a bit better

Classroom Rule of 72 is still the usual shortcut.

96. If two friends save the same monthly amount, the one who starts 10 years earlier

Tap A, B, C or D.

Answer: D) usually ends far ahead even at the same rate

The extra years are extra compounds.

97. Interest-on-interest is another name for

Tap A, B, C or D.

Answer: A) compound interest

That is the whole idea.

98. A compound-interest question in exams often hides

Tap A, B, C or D.

Answer: C) whether the rate is per year and how many times it compounds

Underline n and t first.

99. The official source for “compound interest” (learn desk, item 1) is

Tap A, B, C or D.

Answer: D) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

100. The official source for “compound interest” (learn desk, item 2) is

Tap A, B, C or D.

Answer: B) the authority or standard named on this page’s explainer

GKSchools English practice is original — not an official script.

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