Question

What is the sum of the first 20 consecutive odd numbers?

Answer 1

the first 20 consecutive odd numbers are:

1  +  3  +  5  +  7  +  9  +  11  +  13  +  15  +  17  +  19  +  21  +  23  +  25  +  27  +  29  +  31  + 33  +  35  +  37  +  39      =    400

Answer 2

1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39 
above are the first 20 odds 
If you add the first to the last you get 40 
If you add the second to the second from last you get 40 
It doesn't matter which numbers you add first so long as you add them all up 
there are 10 pairs of numbers totaling 40 so the sum is 400