How many 4 digit numbers can be formed by the digits 2 4 6 8 once in each numeral?

Answer 1

This question can be answered regardless of what digits are used. If there are four options for the first digit, then there are only 3 options for the second digit, and 2 options for the third. There are no options left for the fourth and final digit. So, the answer is 4! (or four factorial).

Answer 2

== Four factorial== 4! = 4 factorial 4! = 4 x 3 x 2 x 1 = 24