Important Maths Formulas of Simple Interest
Let Principal = P, Rate = R% per annum (p.a.) and Time = T years
Simple Interest(S.I.) 

Amount(A)  A = P + S.I. 
Principal  
Rate  
Time 
Important Maths Formulas of Compound Interest:
Let Principal = P, Rate = R% per annum (p.a.) and Time = n years
Then, the amount A and compound Interest C.I. is:
When the interest is compounded yearly  
When the interest is compounded half yearly  
When the interest is compounded quarterly  
When interest is compounded annually, but time is a fraction, say


When the rates are different for different years say, R_{1}%, R_{2}%, R_{3}% per annum for first, second and third years, respectively 