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A man saves Rs. 200 in each of the first...

A man saves Rs. 200 in each of the first three months of his service. In each of the subsequent months his saving increases by Rs, 40 more than the saving of immediately previous month. His total saving s from the start of service will be Rs. 11040 after

A

21 months

B

18 months

C

19 months

D

20 months

Text Solution

Verified by Experts

The correct Answer is:
A
Total savings=200+200+200+240+280+… to n months
Given total savings=11040
`rArr400+(n-2)/2(400+(n-3)cdot40)=11040`
`rArr(n-2)(140+20n)=10640`
`rArr20n^(2)+100n-280=10640`
`rArrn^(2)+5n-546=0`
`rArr(n-21)(n+26)=0`
`rArrn=21 as nne-26`
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