A certain sum of money is invested for one year at a certain rate of simple interest. If the rate of interest were 3% higher, then revenue earned would be 20% higher. What is the rate of interest? Choose the most appropriate option.
A) 24% p.a.  B) 4% p.a.  C) 12% p.a.  D) 15% p.a.  E) 18% p.a.
Let the rate of interest be x%.   Now it will be (x + 3)%   % increase = (((x + 3) - x)/x) * 100 = 20   =&gt; x = 15   ANSWER:15% p.a.
<result>D</result>
A certain sum of money is invested for one year at a certain rate of simple interest. If the rate of interest were 3% higher, then revenue earned would be 20% higher. What is the rate of interest?