The formula for calculating simple interest (S.I.) is :
S.I. = (P x r x t)/100
where P is principal, r is annual rate in %, and t is time in years.
Calculating S.I. given P, r and t is very easy.
Since this formula has four (4) variables, given any three, the fourth one can be calculated, e.g. calculate t given S.I., P and r.
