Can anyone help with two math problems?

Question

Please state a solution and explain how you arrived at it. thanks!

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

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

Answer 1

0 + 1 - 2 + 3 - 4 + 5 - 6 + ...- 98 + 99 - 100

= (0+1) + (-2+3) + (-4+5) + ... (-98+99) - 100

= 1 + 1 + 1 + 1 + ... +1 - 100

There were 50 pairs of numbers, so we have 50 - 100 = -50.

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

= (0+100) + (1+99) + (2+98) + (3+97) + ... (49+51)

= 100(50)

=  5050