Question

How many four-digit numbers can be made from the following digits {1, 3, 5, 7} if no digits are repeated?

Answer 1

We have 4 choices for the first number, 3 choices for the second number, 2 choices for the third number, and 1 choice for the fourth number.

So 4 × 3 × 2 × 1 = 24 four-digit numbers can be made.