Correct Answer - Option 1 : 7 months
Given:
⇒ Total investment of M = 450 × 6 + 300 × 6 = Rs.4500
Let the time after which N adds Rs.100 to his investment be p.
⇒ Total investment of N = 300 × a + 540 × (12 - a) = Rs.(6480 - 240a)
Total profit of M and N = 1085 × 2 = 2170
The difference between the shares of N and M = Rs.70
Solving,
⇒ Profit share of M = Rs.1050
⇒ Profit share of N = Rs.1120
Ratio of their profit shares = 1050 : 1120 = 15 : 16
Then,
⇒ 4500 : (6480 - 240a) = 15 : 16
Solving,
⇒ a = 7
∴ After 7 months, N adds Rs.240 to his investment.