1
$\begingroup$

What is the value of $$1+2+3-4+5+6+7-8+9+10+11+12...+97+98+99-100 \ ?$$ Any help is appreciated, thank you!

I added the terms as an AP then subtracted 10 then all the numbers that were missed out, not sure if this is right though.

  • 1
    This looks like $(1 + 2 + ... + 100) = 5050$, but with a $-4, -8, -100$, which net a $-8, -16, -200$ to the sum. So $5050- 224$2012-03-21
  • 0
    the pattern continues2012-03-21
  • 0
    the minussing does not only occur in the first few examples2012-03-21
  • 0
    I didn't see that, since you had $+12$ in there... In that case, take $5050$ and subtract two times (*why?*) the series $(4 + 8 + 12 + ... + 100)$2012-03-21

3 Answers 3