
If 7th and 13th terms of an A.P. be 34 and 64 respectively, then its 18th term is
A. 87 B. 88 C. 89 D. 90 Answer: Option CShow Answer
Solution(By Apex Team)
$\begin{array}{l}\text{7th term (a7) = a + 6d = 34}\\
\text{13th term (a13) = a + 12d = 64}\\
\text{Subtracting, 6d = 30 ⇒ d = 5}\\
\text{and a + 12 x 5 = 64}\\
\text{⇒ a + 60 = 64}\\
\text{⇒ a = 64 – 60 = 4}\\
\text{18th term (a18)}\\
\text{= a + 17d}\\
\text{= 4 + 17 x 5}\\
\text{= 4 + 85}\\
\text{= 89}\end{array}$
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