The sum all even natural numbers between 1 and 31 is:
1. 240
2. 16
3. 128
4. 512
240
Required sum = (2 + 4 + 6 + ... + 30) This is an A.P. in which a = 2, d = (4 - 2) = 2 and l = 30. Let the number of terms be n. Then, tn = 30 a + (n - 1)d = 30 2 + (n - 1) x 2 = 30 n - 1 = 14 n = 15 Sn = n (a + l) = 15 x (2 + 30) = 240. 2 2
