Question

Find the number of four-digit numbers which are not divisible by 4?

Answer 1

6750

Explanation:

4 digit numbers are 1000,1001,1002,...,9999

let numbers=n

d=1001-1000=1

9999=1000+(n-1)1

9999-1000=n-1

8999+1=n

n=9000

now let us find the 4 digit numbers divisible by 4

4| 1000

______

| 250

4 |9999

_____

| 2499-3

9999-3=9996

so numbers are 1000,1004,1008,...,9996

a=1000

d=1004-1000=4

let N be number of terms

9996=1000+(N-1)4

9996-1000=(N-1)4

8996=(N-1)4

N-1=8996/4=2249

N=2249+1=2250

so number of 4 digit numbers not divisible by 4=9000-2250=6750