How many numbers between 100 and 999 are divisible by 4?

Try this solution:

1. Note, that 100 is divisible by 4, and 999 is not divisible by it, only 996. This is an arithmetic sequence.

2. a1; a2; a3; a4; ... a (n) the sequence, where a1=100; a2=104; a3=108; a4=112; ... etc., and a (n) = 996. n=?

3. using a formula for n-term of the sequence: a (n) = a1+d (n-1), where a (n) = 996; a1=100 and d=4 (according to the condition ' is divisible by 4'). Then 100+4 (n-1) = 996; ⇒ 4n=900; ⇒ n=225 (including 100).

answer: 225