A man invests Rs.3,000 at the rate of 5% per annum. How much more should he invest at the rate of 8%, so that he can earn a total of 6% per annum?
Explanation:
Using alligation, the ratio of the amounts invested at both the rates = 2 : 1. Since he has invested Rs.3,000 at 5%, he should further invest Rs.1,500 at 8% to earn a total interest of 6% per annum.
Alternative method: Let the amount invested at 8% be Rs. x. Then, 3000×105100+x×108100=(3000 + x)106100
⇒ 0.02x = 30 ⇒ x = 1,500
∴ He should further invest Rs.1,500 at 5% to earn a total interest of 6% per annum.
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