Question

The number of numbers of 4 digits which are not divisible by 5 are ___.

Answer 1

The total number of 4 digits are 9999-999=9000.

Any number whose last digit is 5 or 0 is divisible by 5.

If wxyz is a four digit number then 'w' can take values 1 to 9, and x, y can take values 0 to 9. To be divisible by 5, 'z' can only be 0 or 5.

The numbers of 4 digits number divisible by 5 are $9\times 10\times 10\times 2$=1800. Hence required number of ways are 9000-1800 =7200.

{Since there are 20 numbers in each hundred (1 to 100) divisible by 5. Therefore, from 999 to 9999 there are 90 hundreds, hence the results}.