GMAT GRE SAT MATH:Power of numbers, unit number exercises

What is the sum of all the even numbers bigger than (-10) and smaller than 12?

(a) 2.
(b) 10.
(c) 0.
(d) 8.
(e) 4.

The best answer is B.
This is a series of numbers with a constant spacing between them.
The first number is (-8) and the last is (10), there are 10 numbers altogether.
The formula for such a series is: ((-8 + 10) x 10)/2 = 10.
The second way to answer such a question is to write the numbers and add them.