3-Digit Number Properties and Factors

CAT 2025 Slot 1 · Quantitative Ability · Hard · Number System

This is a hard Quantitative Ability question from the CAT 2025 Slot 1 paper. It tests Number System. The full answer key and a step-by-step explanation are below — try it yourself first, then reveal the solution.

In a 3-digit number NN, the digits are non-zero and distinct such that none of the digits is a perfect square, and only one of the digits is a prime number. Then, the number of factors of the minimum possible value of NN is

Answer

6

Explanation

Allowed non-zero, distinct digits that are NOT perfect squares (1,4,91, 4, 9 excluded): {2,3,5,6,7,8}\{2, 3, 5, 6, 7, 8\}. Primes in this set: {2,3,5,7}\{2, 3, 5, 7\}. Non-primes in this set: {6,8}\{6, 8\}.

Since exactly one digit is prime and the other two are non-prime, the two non-prime digits MUST be 66 and 88. The single prime digit can be selected from {2,3,5,7}\{2, 3, 5, 7\}.

To minimize NN, we want the smallest hundreds digit. Choosing prime 22 as the hundreds digit gives N=268N = 268. Prime factorization of 268=22×67268 = 2^2 \times 67. Number of factors = (2+1)×(1+1)=3×2=6(2+1) \times (1+1) = 3 \times 2 = 6.

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