Question

how many number can be formed using the digits 1,7,4, and 5 exactly once ​

Answer 1

Answer:

1475 ,1457,1547,1574 ,1754 ,1745

Answer 2

Total digits = 4

Given that, the digits cannot be repeated.

Now,

Ones place can be filled in 4 ways.

Tens place can be filled in 3 ways.

Hundreds place can be filled in 2 ways.

Thousands place can be filled in 1 way.

Therefore, total numbers which can be formed = 4 × 3 × 2 × 1

= 24.

Hope it helps.