The fifth term of an A.P is 24 and the eleventh term is 96. Find the first term.
A
12
B
4
C
-12
D
-24
Verified Correct Answer: D.
Step-by-Step Mathematical Solution
U5 = 24, n = 5 and U11 = 96, n = 11
Un = a + (n-1)d
24 = a + (5-1)d imply 24 = a+4d .....eqn1
96 = a + (11-1)d imply 96 = a+10d ...eqn2
eqn1 - eqn2 -72 = -6d
d = 72/6 = 12
but 24 = a+4d
24 = a + 4(12)
24 = a + 48
a = 24-48
a = -24
Source: Myschool Past Questions Archive (Record #9275)