Respuesta :

Madzmom
1 + 2 + 3 + ... + n = n(n + 1)/2.

So:

13 + 14 + 15 + ... + 37
= (1 + 2 + 3 + ... + 37) - (1 + 2 + 3 + ... + 12)
= 37(37 + 1)/2 - 12(12 + 1)/2
= 625.

Since there are 25 integers, the average is 625/25 = 25.