A.P Actual Question in NCAT 2023

NCATadmin

December 27, 2023

1. Find the sum of series 1 + 3.5 + 6 + 8.5 + _ _ _ + 101
a. 2091
b. 2081
c. 1091
d. 2191

EXPLANATION

Sn = (n/2)(a1 + an)

a1 = 1

But we need first to determine n.

To do that we need d:

d = 3.5-1 = 6-3.5 = 8.5-6 = 2.5

an = a1 + (n – 1)∙d

101 = a1 + (n – 1)∙2.5

Solve that and get n = 41

Sn = (n/2)(a1 + an)

S41 = (41/2)(1 + a41)

S41 = (41/2)(1 + 101)

S41 = (41/2)(102)

S41 = 2091