If the compound interest on a certain sum for 2 years in Rs. 80.80 and the simple interest Rs. 80; then the rate of interest per annum is	Choose the correct answer
A) 2% B) 1% C) 3% D) 4% E) 5%
Explanation:   Let the sum be P and Rate of Interest be R% per annum   Simple Interest on Rs.P for 2 years = 80   PRT/100 = 80   (PR × 2)/100 = 80   PR/50 = 80   PR = 4000 - -- (equation 1)   Compound Interest = P(1 + R/100)T - P   = P(1 + R/100)2 - P   = P[(1 + R/100)2 - 1] = P[(1 + 2R/100 + R2/10000) - 1] = P(2R/100 + R2/10000)   = 2PR/100 + PR2/10000   = 2PR/100 + (PR × R)/10000   = [2 × 4000]/100 + (4000 × R)/10000 ( substituted the value of PR from equation 1)   = 80 + 0.4R   Given that compound interest = Rs.80.80   =&gt; 80 + 0.4R = 80.80   =&gt; 0.4R = 0.80   =&gt; R = 0.80/0.4= 
<gadget id="calculator">0.80/0.4</gadget>
<output>2</output>
2%   2%nswer: Option 2%
<result>A</result>
If the compound interest on a certain sum for 2 years in Rs. 80.80 and the simple interest Rs. 80; then the rate of interest per annum is