A man saves Rs. 200 in each of the first three months of his service. In each of the subsequent mont

Question

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 from the start of service will be Rs. 11040 after

Accepted Answer

1 2 3 4 5 6 .....
200 200 200 240 280 ..... .....
Sum = 11040
120 + 80 + 160 + 40 + 200 + 240 + .... = 11040

[2a + (n - 1)d] + 80 + 40 = 11040

[2a + (n - 1)40] = 10920
n [Â 6 + n - 1 ] = 546
n (n + 5) = 546
n = 21

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