Question

Each two digit number is written on a paper slip and these are all put in a box. What is the probability that the digits of a number drawn is a prime number? What if three-digit numbers are used instead

Answer 1

Answer:

If product of two digits is prime, one of the digits will be 1 and the other digit a prime number. There are 4 digits which are prime. They are 2, 3, 5, 7.

so, the numbers are 12, 13, 15, 17, 21, 31, 51, 71. I.e. total numbers are 8.

total count of 2 digit numbers are 90.

so, probability = 8 / 90