Interview Q&A / Aptitude

1. How many trailing zeros does 250! have?

   62. Each trailing zero needs a pair of 2 and 5, and 5s are scarcer, so count the 5s: 250/5 = 50, 250/25 = 10, 250/125 = 2 (take whole parts), total 62.

   BeginnerQuick answer1 min read
2. What digit x makes the number 4x6723 divisible by 11?

   x = 2. For divisibility by 11, the difference between the sum of digits in odd places and in even places (counted from the right) must be 0 or a multiple of 11. Here that difference is x - 2, so x = 2, giving 426723 = 11 x 38793.

   BeginnerQuick answer1 min read
3. What is the unit digit of 7^95?

   The answer is 3. Unit digits of powers of 7 repeat in a cycle of four (7, 9, 3, 1). 95 leaves remainder 3 when divided by 4, so 7^95 ends like 7^3, which ends in 3.

   BeginnerQuick answer1 min read