Simple Interest

Simple Interest on P Dollars at interest rate r (expressed as a decimal) over time period t is

Example:- The Simple Interest on $400 for 3 months at 5% per annum Simpe interest would be
I=Prt

Hence Simple Interest on $400 for 3 months at 5% pa Simple Interest is 5 Dollars.

Compound Interest

The amount A, or future value, of principal P invested at interest rate r (expressed as decimal) compunded m times per year for t years is

where

,

the interest rate per compounding period, and n=mt, the number of compunding periods.

For example, Compound interest for $400 at the rate of 10% per annum compounded half yearly for 1 year would be calculated as follows:-
n=2 (1year = 2 half years).
i=10% pa = 5% per half year

Therefore, Compound Interest = $441-$400 = $41

Annuity
The future value of an Ordinary Annuity is

where R is the periodic payment, i the interest rate per period, and n the number of periods. In an ordinary annuity, the payment is made at the end of each period.

The present value of an ordinary annuity is

Profit and Loss
SP=Selling Price, CP=Cost Price