# Math Help - 2 problems, thanks!

1. ## 2 problems, thanks!

1. 0 + 1 - 2 + 3 - 4...100=___

2. 0 + 1 + 2 + 3 + 4 +...+ 98 + 99 + 100=_____

state solution and explanation of how you got to the solution,

thanks!

2. Originally Posted by Alana0001
1. 0 + 1 - 2 + 3 - 4...100=___

2. 0 + 1 + 2 + 3 + 4 +...+ 98 + 99 + 100=_____

state solution and explanation of how you got to the solution,

thanks!
In both cases you're expected to know and use the formula for the sum of an arithmetic series.

Note that the first one can be re-arranged as (1 + 3 + 5 + .... + 99) - (2 + 4 + 6 + ...... + 100).

3. Originally Posted by Alana0001
1. 0 + 1 - 2 + 3 - 4...100=___

2. 0 + 1 + 2 + 3 + 4 +...+ 98 + 99 + 100=_____

state solution and explanation of how you got to the solution,

thanks!
Use these formulas:
$1+2+3+...+n=\frac{n(n+1)}{2}$
$1+3+5+...+n=\left(\frac{n+1}{2}\right)^2$