What is the thirteenth term of an arithmetic series if the third and tenth terms are 11 and 60 respectively?
A74
B77
C81
D84
Answer:
C. 81
Read Explanation:
Let tge first term be a, and common difference be d;
3rd term = a + 2d = 11 .......(1)
10th term= a + 9d = 60 .......(2)
(2) - (1) =
7d = 49
d = 49/7 = 7
a + 3d = a + 3 × 7 = 11
a = 11 - 14 = -3
13th term=a +12d
= -3 + 12 × 7
= -3 + 84
= -81
