RD Sharma Solutions for Class 7 Chapter 13 “Simple interest” – Simple interest is a quick and easy method of calculating the interest charge on loan. Simple interest is determined by multiplying the daily interest rate by the principal by the number of days that elapse between payments—the concept of simple interest, how to calculate simple interest and practice test on simple interest. The concepts covered in this chapter help to find simple interest when principal, rate and time are given, using formula.