Question

Find the sum of 1+2-3+4+5-6+7+8-9+...+97+98-99

Answer 1

Hi,

Explanation:

Let's make group of 3 numbers

1+2-3=0

4+5-6=3

7+8-9=6

...

97+98-99=96

s=1+2-3+....+97+98-99=0+3+6+..+96=3*(0+1+2+3+...+32)

=3*(32+0)*33/2

=1584