A man invested a sum of N280.00 partly at 5% and partly a...
A man invested a sum of N280.00 partly at 5% and partly at 4%. if the total interest is N12.80 per annum, find the amount invested at 5%
14.00
120.00
140.00
160.00
Correct answer is D
Let the amounts invested at 4% and 5% respectively be x and y.
∴
Interest on x = \frac{x \times 4 \times 1}{100} = 0.04x
Interest on y = \frac{y \times 5 \times 1}{100} = 0.05y
\therefore 0.04x + 0.05y = 12.80
\implies 4x + 5y = 1280 ... (ii)
From (i), x = 280 - y.
Put into (ii), 4(280 - y) + 5y = 1280
1120 - 4y + 5y = 1280
1120 + y = 1280 \implies y = 1280 - 1120 = N160
\therefore N160 was invested at the rate of 5% per annum.
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