Question

If 16th term of the series X, 3.5, 3.25, 3.....is zero, then sum of 1st 16 term of the series is
(a) 90
(b) 30
(c)-30
(d)0​

Answer 1

n = 16

d = 3.25 - 3.5 = -0.25

a = 3.5 + 0.25 = 3.75

Sum = n/2 [2a + (n - 1) d]

= 16/2 [7.5 + 15 (-0.25)]

= 8 (7.5 - 3.75]

= 8 × 3.75

Sum = 30