A sum of money becomes 7/6 of itself in 7 years at a certain rate of simple interest. The rate per annum is?  Choose the correct choice from the following choices
A) 50/13  B) 50/17  C) 50/19  D) 50/21  E) 50/23
Let sum = x. Then, amount = 7x/6   S.I. = 7x/6 - x = x/6; Time = 7 years.   Rate = (100 * x) / (x * 6 * 7) = 50/21 %.   Answer:50/21
<result>D</result>
A sum of money becomes 7/6 of itself in 7 years at a certain rate of simple interest. The rate per annum is?