Question

Three-digit numbers are to be formed from 1,2,3,4,5,6,7,8 & 9. If repetition of digits is not allowed; a). How many numbers can be formed. b). How many numbers divisible by 5 can be formed?​

Answer 1

• a) 504,
• b) 56

Explanation:

Let the number is xyz.

There are 9 options for x, 8 options for y and 7 options for z since no repetition is allowed.

a)

Total number of options:

• 9*8*7 = 504

b) Since number is divisible by 5, we must have z = 5. Then we have 8 options for x and 7 options for y.

Total number of options:

• 8*7*1 = 56