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If the sum of first 10 terms of an A.P. ...

If the sum of first 10 terms of an A.P. is 4 times the sum of its first 5 terms, then find the ratio of first term and common difference.

A

`(1)/(2)`

B

2

C

`(1)/(4)`

D

4

Text Solution

Verified by Experts

The correct Answer is:
A
According to the question, for AP
`S_(10)=4S_(5)`
`(10)/(2)(2a+9d)=4*(5)/(2)(2a+4d)[" by " S_(n)=(n)/(2)[2a+(n-1)d]]`
`10a+45d=20a+40d`
`implies 10a=5d " " implies (a)/(d)=(1)/(2)`
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Knowledge Check

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