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Class 10 Mathematics

Important questions

4 Practice Questions — The answers are hidden. Reveal them to check your answers. The Timed Test will be available in Phase 3.

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Chapter: Ch. 1

Q.1MCQeasyImportant

Euclid’s division lemma states that for integers a and b (b > 0) there exist unique integers q and r such that:

  • A. a = bq + r, 0 ≤ r < b
  • B. a = bq − r, r > b
  • C. a = q + r
  • D. a = b + q + r
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Correct option: A — a = bq + r, 0 ≤ r < b

This is the starting tool for the Euclidean algorithm to find HCF.

Q.2MCQmediumImportant

HCF of 26 and 91 is:

  • A. 13
  • B. 7
  • C. 26
  • D. 1
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Correct option: A — 13

91 = 26 × 3 + 13; 26 = 13 × 2 + 0, so HCF is 13.

Q.3Short answermediumImportant

Prove that √3 is irrational (outline the usual contradiction method).

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Assume √3 = p/q in lowest terms. Then p² = 3q² so p is divisible by 3; write p = 3k. Then 9k² = 3q² ⇒ q² = 3k², so q is also divisible by 3. This contradicts lowest terms. Hence √3 is irrational.

The same pattern works for √2, √5, √7.

Q.4Long answermediumImportant

Use Euclid’s algorithm to find HCF(405, 252) and write 405 and 252 as products of primes.

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405 = 252 × 1 + 153
252 = 153 × 1 + 99
153 = 99 × 1 + 54
99 = 54 × 1 + 45
54 = 45 × 1 + 9
45 = 9 × 5 + 0
HCF = 9.
405 = 5 × 3⁴; 252 = 2² × 3² × 7. Common primes give 3² = 9.

Prime factorisation is a check, not a replacement, for the lemma method in exams.

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These practice sets use original GKSchools wording — they are not a verbatim dump of the NCERT textbook. “Important” means high-weight practice for the chapter, not a claim that these are previous-year exam questions.

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