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

Options

A. 19 months
B. 20 months
C. 21 months
D. 18 months

Answer

C

Explanation

Let the time taken to save Rs. 11040 be `(n+3)` months.
For first 3 months, he saves Rs. 200 each month.
`:. " In " (n+3)" month "`
`3xx200+(n)/(2)[2(240)+(n-1)x40]=11040`
`implies 600+(n)/(2)[40(12+n-1)]=11040`
`implies 600+20n(n+11)=11040`
`implies n^(2)+11n-522=0`
`implies (n-18)(n+29)=0`
`:. n=18, " neglecting " n=-29`
`:. " Total time " =n+3=21 " months "`.