Question: how many 3 digit combinations with 5 numbers?
Answer: Now start again with 2 as the first digit. The smallest is 21345, the largest is 25431 and again there are 24 possibilities. Repeat this process again with 3 as the first digit, then 4 as the first digit and finally 5 as the first digit. In total you will find 5 × 24 = 120 possibilities.