Question

If the monthly instalment is ₹ 100 and the rate of interest is 8%, in how many months Joseph will receive ₹ 52 as interest?

विकल्प

• 18

• 30

• 12

• 6

Answer 1

12

Explanation:

Given:

I = ₹ 52

P = ₹ 100

r = 8%

`I = P xx (n(n + 1))/(2 xx 12) xx R/100`

∴ `I = 100 xx (n(n + 1))/(2 xx 12) xx 8/100`

`52 = (n(n + 1))/24 xx 8`

`52 = (n(n + 1))/3`

n(n + 1) = 52 × 3

n(n + 1) = 156

n² + n – 156 = 0

n² + 13n – 12n – 156 = 0

n(n + 13) – 12(n + 13) = 0

(n + 13)(n – 12) = 0

n = –13 or n = 12

Since the number of months cannot be negative.

∴ n = 12 months