Question

Raj saves some amount every month. in first three months he saves rs200, rs250, rs300 respectively. how much total amount saved in 17months? complete the following flow chart and rewrite.

Answer 1

A.P. = 320, 360, 400...

a = 320

d = 360 - 320 = 40

Sn = 20000

Formula =>

Sn = n/2(2a + (n -1)d)

20000 = n/2(2×320 + (n - 1)40)

20000 = n(320 + (n - 1)20)

20000 = n(320 + 20n - 20)

20000 = 300n + 20n²

20n² + 300n - 20000 = 0

20(n² + 15n - 1000) = 0

n² + 15n - 1000 = 0

n² + 40n - 25n - 1000 = 0

n(n + 40) - 25(n + 40) = 0

(n + 40)(n - 25) = 0

n = -40 or 25

Months can't be negative so it should be positive.

Therefore in 25 months it will save rs 20000