Question

How many 4-digit numbers can be formed from the digits 2, 3, 8 and 9?

Answer 1

There are 4 digits.

Case I) If the repitition of the digits are not allowed then,

For the 1st place there are four options, for the 2nd place there are three options, for the 3rd place there are 2 options and for the 4th place there are 1 option. So, the number of 4-digit numbers

= 4 × 3 × 2 × 1 = 24

Therefore, the number of 4-digit numbers = 24

Case II) If the repitition of the digits are allowed then,

All places there are four options, So, the number of 4-digit numbers = 4 × 4 × 4 × 4 = 256

Therefore, the number of 4-digit numbers = 256