Question

Find the sum of the series 1 + 2 + 4 + 5 + 7 + 8 + 10 + 11 + ... + 299, which is the sum of the integers from 0 to 300, omitting the multiples of 3.

Answer 1

well, I suspect that you can find the sum of the arithmetic sequence starting with 1 and ending at 299 with d = 1

then you need to find the sum of the arithmetic sequence
3 6 9 12 ....... 297
from 3 to 297 with d = 3

then subtract

see:
http://www.mathsisfun.com/algebra/sequences-sums-arithmetic.html