The 4th term of an A.P. is 13 while the 10th term is 31. Find the 24th term.
A
89
B
75
C
73
D
69
Verified Correct Answer: C.
Step-by-Step Mathematical Solution
a + 3d = 13 .......... (1)
a + 9d = 31 .......... (2)
(2) - (1): 6d = 18
d = 18/6 = 3
From (1), a + 3(3) = 13
a + 9 = 13
a = 13 - 9 = 4
Hence,
T24 = a + 23d
T24 = 4 + 23(3)
T24 = 4 + 69
T24 = 73
Source: Myschool Past Questions Archive (Record #27012)