Find the following sum: 2+4+6+8+10...+400
Please help ASAP!!! :(
note that your sum is
2(1+2+3+...+...200)
Now recall Gauss's trick of pairing up the ends of the series.
1+200 = 201
2+199 = 201
and so on. There are 100 pairs of numbers which add up to 201. So the entire sum is
2(100*201)
Just for reference, the sum
1+2+3+...+n = n(n+1)/2