The 4th term of an A P is 13 while the 10th ter... - JAMB Mathematics 1995 Question
The 4th term of an A.P. is 13 while the 10th term is 31. Find the 21st term.
A
175
B
85
C
64
D
45
correct option: c
a + 3d = 13
a + 9d = 31
6d = 18
= d = 3
a = 13 - 9
= 4
a + 20d = 4 + (20 x 3)
= 64
a + 9d = 31
6d = 18
= d = 3
a = 13 - 9
= 4
a + 20d = 4 + (20 x 3)
= 64
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