How to use simple method to calculate mathematics 2 + 4 + 6 + ·· + 18 + 20

How to use simple method to calculate mathematics 2 + 4 + 6 + ·· + 18 + 20

The original formula = (2 + 20) + (4 + 18) + (6 + 16) + (8 + 14) + (10 + 12) = 22 * 5 = 110