In an A.P. if first term is 4,9th term is 20, then 15th term is
In an A.P. if first term is 4,9th term is 20, then 15th term is
A) 32
B) 36
C) 16
D) 18
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Correct option is (A) 32
Given that \(a_1=4\;\&\;a_9=20\)
\(\because a_n=a+(n-1)d\)
\(a_9=a+8d\)
\(\therefore20=4+8d\)
\(\Rightarrow8d=20-4=16\)
\(\Rightarrow d=\frac{16}8=2\)
\(a_{15}=a+14d\)
\(= 4+14\times2\)
\(=4+28=32\)
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