KIRA did not have to add the odds and the evens. It was a trick question. Each difference is one.
one times five = five
By the way, story of Gauss in elementary school:
add numbers from 1 to 100 :
instant reply: average = 50.5
50.5 * 100 = 5050
alternate reply
1 + 2 + 3 ...... 100
+
100 + 99 + 98 ..... 1
= 101 + 101 + 101 .... +101
so
2 S = 100*101 = 10100
so s = 5050