Question

The sum of all positive integers less than 300 which are not divisible by 3.

Answer 1

30000

Explanation:

all positive integers less than 300 (300 exclusive)

1,2,3,4,5..........149,150,151.......296,297,298,299

there are (1+299) (2+298) (3+297)...(149+151) 149 pairs of 300 + 150

300 x 149 + 150 = 44850

all positive integers less than 300 which are divisible by 3

3,6,9,12..........294,297 i.e. 3 x (1,2,3,4.......49,50,51.....97,98,99)

3 x ((100 x 49) + 50) = 3 x 4950 = 14850

Answer: 44850 - 14850 = 30000