The sum of even numbers between 1 and 31 is:

Let S_n = (2 + 4 + 6 + ... + 30). This is an A.P. in which a = 2, d = 2 and l = 30

Let the number of terms be n. Then,

a + (n - 1)d = 30

     2 + (n - 1) x 2 = 30

    n = 15.

Sn =	n	(a + l)	=	15	x (2 + 30) = (15 x 16) = 240.
	2			2