permutation

Question

How many numbers without repeating the number or digit less than 1000 are divisible by 5 can be formed ?

Answer 1

Compare 3 problems:

Answer 2

since repetation of digit is not allowed no of digit  =(any of the remaining 8 digits not used in unit and tenth place incuding 0 )(it could any of the 9 digits which is not the digit used in unit place)(it could be 0 or 5 as the no should be divisible by 5)+a 1 digit no 5

note; 2 digit no is calculated because the msb of the  3 digit no can be 0.

 =             =(8 ways)(9ways)(2 ways)

                =(144)+1=145

Answer 3

No of three digit numbers

1)ending with 5 =9*8=72

2)ending with 0=8*8=64

No of two digit numbers

1)ending in 5=9

3)ending in 0=8

One digit number=1

So total numbers=64+72+17+1=154

Comments

Shouldn't we count 0 ?