Find the rate at Simple interest, at which a sum becomes four times of itself in 15 years. Choose the correct choice from the following.
A) 10%
B) 20%
C) 30%
D) 40%
E) 50%
Explanation:   Let sum be x and rate be r%   then, (x*r*15)/100 = 3x [important to note here is that simple interest will be 3x not 4x, beause 3x+x = 4x]   =&gt; r = 20%   Option 20%
<result>B</result>
Find the rate at Simple interest, at which a sum becomes four times of itself in 15 years.