If the 10^(th) term of an A.P. is 1/5 a...

If the `10^(th)` term of an A.P. is `1/5` and its `20^(th)` term is `1/3` , then the sum of its first 150 terms is:

A

159

B

161

C

164

D

167

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The correct Answer is:

B

`T_(10) = 1/5 = a + 9d" "....(1)`
`T_(20) = 1/3 = a+19d" "....(2)`
`a=6/(75) , d=1/(75)`
Hence , `S_(150) =(150)/2 [(12)/(75) + (149)/(75) ] =161`

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