Question

how many numbers greater than 100 can be formed using the digits 1,2,3,4,5,if no digits may be repeated.

Answer 1

Your numbers could be either 3 digits, 4 digits or all 5 digits
3 digits: 5*4*3 = 60
4 digits: 5*4*3*2 = 120
5 digits: 5*4*3*2*1 = 120
total = ...