Discussion

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, $3000\times \frac{105}{100}+x\times \frac{108}{100}=(3000 + x)\frac{106}{100}$

⇒ 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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