A sum of Rs. 1550 was lent partly at 5% and partly at 8% p.a. simple interest. The total interest received after 3 years was Rs. 300. The ratio of the money lent at 5% to that lent at 8% is:

Explanation:-

Let the sum lent at 5% be Rs. x and that lent 8% be Rs. (1550 - x).
Then,
$$\eqalign{ & = \left( {\frac{{x \times 5 \times 3}}{{100}}} \right) + \left[ {\frac{{\left( {1550 - x} \right) \times 8 \times 3}}{{100}}} \right] = 300 \cr & \Leftrightarrow 15x - 24x + \left( {1550 \times 24} \right) = 30000 \cr & \Leftrightarrow 9x = 7200 \cr & \Leftrightarrow x = 800. \cr & \therefore {\text{Required ratio}} = 800:750 \cr & = 16:15 \cr}$$