Question

Joan wants to set a 4-digit unlock code for her mobile phone. She plans to use only odd numbers and to make sure that no number is used more than once. How many different unlock codes are possible.

Answer 1

Answer: 120

Explanation:

There are 5 digits that are odd, 1 3 5 7 9

There are 5 possibilities for the first digit, 4 for the second, 3 for the third, and 2 for the last, so there are 5 x 4 x 3 x 2 = 120