Find the total number of prime factors in the expression 411×75×112

2023

Find the total number of prime factors in the expression 411×75×112

  1. A.

    18

  2. B.

    31

  3. C.

    29

  4. D.

    20

Attempted by 3 students.

Show answer & explanation

Correct answer: C

When a number is written as a product of prime powers p1a×p2b×..., the total number of prime factors counted with multiplicity (repetition) is simply the sum of the exponents a+b+... — each exponent tells you how many times that prime is repeated in the product.

  1. 4 is not itself a prime number, so first rewrite it in terms of its prime base: 4 = 22.

  2. Apply the power-of-a-power rule (multiply the exponents, not add them): 411 = (22)11 = 22×11 = 222, so this term contributes 22 factors of 2.

  3. 75 is already prime, contributing 5 factors of 7.

  4. 112 is already prime, contributing 2 factors of 11.

  5. Add the contributions from every prime term: 22 + 5 + 2 = 29.

Cross-check: rewriting the whole expression purely in prime bases gives 222×75×112 — counting the exponents once more (22, 5, 2) and re-adding them confirms the same total of 29 prime factors.

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