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Q15·CSAT · Prelims 2025

Maximum power of 35 dividing a product

NumericalFactors & PowersNumber theoryMedium

Question

What is the maximum value of n such that 7 × 343 × 385 × 1000 × 2401 × 777777 is divisible by 35^n?

Options

a

3

b

4

Answer
c

5

d

7

Explanation

To find the maximum power of 35 that divides the product, we must find the prime factorization of the given numbers. Since 35 = 5 × 7, we count the total available powers of 5 and 7. 385 = 5^1 × 7^1 × 11. 1000 = 10³ = 2³ × 5³. Total powers of 5 = 1 + 3 = 4. Since there are clearly many more powers of 7 (343=7³, 2401=7^4, plus multiples of 7 in 385 and 777777), the limiting prime factor is 5. The maximum number of 35s we can form is dictated by the smaller exponent, which is 4. Thus, n = 4.

When finding the maximum power of a composite number C = p × q dividing a product, find the exponents of p and q in the prime factorization; the smaller exponent dictates the maximum power.

Answer: (b).

Question details

Year

2025

Paper

CSAT

Question

Q15

Section

Numerical Ability

Sub-topic

Factors & Powers

Type

Number theory

Difficulty

Medium

Source hint

Number theory

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