Q1: The sum all even natural numbers between 1 and 31 is:
A 240
B 128
C 16
D 512
ANS:C - 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