The fifth term of an A p is 24 and the eleventh... - JAMB Mathematics 2008 Question
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
correct option: d
In = a + (n - 1)d
24 = a + (5 - 1)d
24 = a + 4d.......(i)
96 = a + (11 - 1)d
96 = a + 10d.......(ii)
a = 24 - 4d.......(iii)
96 = 24 - 4d + 10d
96 = 24 + 6d
96 - 24 = 6d
72 = 6d
d = \(\frac{72}{6}\)
d = 12
a = 24 - 4d
a = 24 - 4 x 12
a = 24 - 48
a = -24
24 = a + (5 - 1)d
24 = a + 4d.......(i)
96 = a + (11 - 1)d
96 = a + 10d.......(ii)
a = 24 - 4d.......(iii)
96 = 24 - 4d + 10d
96 = 24 + 6d
96 - 24 = 6d
72 = 6d
d = \(\frac{72}{6}\)
d = 12
a = 24 - 4d
a = 24 - 4 x 12
a = 24 - 48
a = -24
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