Question

Work out: 1 - 2 + 3 - 4 + 5 - 6 + 7 - 8 + ...... + 1599 - 1600

Answer 1

$1-2+3-4+5-6+7-8+1599-1600$

Add and subtract from left to right.

$1-2=-1 \ \textgreater \ -1+3-4+5-6+7-8+1599-1600 \ \textgreater \ -1+3=2$

$2-4+5-6+7-8+1599-1600 \ \textgreater \ 2-4=-2$

$-2+5-6+7-8+1599-1600 \ \textgreater \ -2+5=3$

$3-6+7-8+1599-1600 \ \textgreater \ 3-6=-3$

$-3+7-8+1599-1600 \ \textgreater \ -3+7=4$

$4-8+1599-1600 \ \textgreater \ 4-8=-4 \ \textgreater \ -4+1599-1600$

$-4+1599=1595 \ \textgreater \ 1595-1600 \ \textgreater \ 1595-1600=-5$

Therefore our answer is -5.

Hope this helps!