A sum was invested at simple interest at a certain interest for 2 years. It would have fetched Rs. 60 more had it been invested at 2% higher rate. What was the sum?

Let the rate be R at which Principal P is invested for 2 years.
According to question,
{Interest at Rate (R + 2)}% - (interest at rate R%) = Rs. 60
$$\frac{{\left( {P \times 2 \times \left( {R + 2} \right)} \right)}}{{100}} - $$     $$\frac{{\left( {P \times 2 \times R} \right)}}{{100}}$$   $$ = 60$$
$$\eqalign{ & \frac{{ {2PR + 4P - 2PR} }}{{100}} = 60 \cr & 4P = 60 \times 100 \cr & {\text{Or}},P = \frac{{60 \times 100}}{4} \cr & {\text{Hence}},P = {\text{Rs}}{\text{.}}\,1500 \cr} $$