Question

(a) Find the common difference of an A.P. whose first term is 5 and the number of terms is 30 and sum 1455.

Answer 1

Sum = n/2[2a + (n - 1)d] where a = first term, n = number of terms and d = common difference

(a) 30/2(2 x 5 + (30 - 1) x d) = 1455
10 + 29d = 1455 / 15
29d = 97 - 10
d = 87 / 29 = 3

(b) 7/2(2 x 9 + (7 - 1)d) = 0
18 + 6d = 0
6d = -18
d = -3