Question
If 7th and 13th terms of an A.P. be 34 and 64 respectively, then its 18th term is
Answer: Option C
7th term (a7) = a + 6d = 34
13th term (a13) = a + 12d = 64
Subtracting, 6d = 30 ⇒ d = 5
and a + 12 x 5 = 64
⇒ a + 60 = 64
⇒ a = 64 – 60 = 4
18th term (a18)
= a + 17d
= 4 + 17 x 5
= 4 + 85
= 89
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7th term (a7) = a + 6d = 34
13th term (a13) = a + 12d = 64
Subtracting, 6d = 30 ⇒ d = 5
and a + 12 x 5 = 64
⇒ a + 60 = 64
⇒ a = 64 – 60 = 4
18th term (a18)
= a + 17d
= 4 + 17 x 5
= 4 + 85
= 89
Was this answer helpful ?
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