MCQEasyJEE 2026Applications of P&C

JEE Mathematics 2026 Question with Solution

The largest value of nn, for which 40n40^n divides 60!60!, is

  • A

    1313

  • B

    1111

  • C

    1414

  • D

    1212

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: We need the largest value of nn such that 40n40^n divides 60!60!.

Find: The maximum integer nn.

Prime factorize the base:

40=23×540 = 2^3 \times 5

So,

40n=23n×5n40^n = 2^{3n} \times 5^n

Now find the powers of 22 and 55 in 60!60! using Legendre's formula.

Power of 22 in 60!60!:

602+604+608+6016+6032=30+15+7+3+1=56\left\lfloor \frac{60}{2} \right\rfloor + \left\lfloor \frac{60}{4} \right\rfloor + \left\lfloor \frac{60}{8} \right\rfloor + \left\lfloor \frac{60}{16} \right\rfloor + \left\lfloor \frac{60}{32} \right\rfloor = 30 + 15 + 7 + 3 + 1 = 56

Power of 55 in 60!60!:

605+6025=12+2=14\left\lfloor \frac{60}{5} \right\rfloor + \left\lfloor \frac{60}{25} \right\rfloor = 12 + 2 = 14

For 40n=23n×5n40^n = 2^{3n} \times 5^n to divide 60!60!, both of the following must hold:

3n563n \le 56

and

n14n \le 14

From the first condition,

n56318n \le \frac{56}{3} \approx 18

Therefore the limiting condition is n14n \le 14, so the largest possible value is 1414.

The correct option is C.

Minimum Bound Trick

Given: 40=23×540 = 2^3 \times 5 and we want the largest nn such that 40n40^n divides 60!60!.

Find: The maximum nn.

Compare required prime powers directly:

  • each factor of 40n40^n needs 3n3n powers of 22
  • and nn powers of 55

In 60!60!, the power of 22 is 5656 and the power of 55 is 1414.

So,

nmin(563,14)n \le \min\left(\frac{56}{3}, 14\right)

Hence,

n14n \le 14

Therefore, the largest value is 1414, so the correct option is C.

Common mistakes

  • Using only the power of 22 and ignoring the power of 55. Divisibility by 40n40^n requires both prime-power conditions to be satisfied. Always compare all primes appearing in the factorization of 4040.

  • Factorizing 4040 incorrectly. Writing 40=22×540 = 2^2 \times 5 is wrong; the correct factorization is 40=23×540 = 2^3 \times 5. This changes the condition on the power of 22.

  • Taking the larger bound instead of the limiting bound. Since both inequalities must hold together, the correct value of nn is determined by the minimum permissible bound, not the maximum.

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