• If a positive whole number is not a perfect square, then its square root is called a surd. A surd cannot be written as a fraction, and is an example of an irrational number.
• When simplifying surds, look for square factors of the number inside the square root and then use
  
• The following formulas may be used to simplify expressions involving surds:
  

The following formulas may be used to simplify expressions involving surds:

• If the denominator of a fraction contains an expression of the form:
  
• The formula for calculating simple interest is:
  I = P × r × t.
  where, I is interest earned, P is principal (amount invested), r is rate of interest (as a decimal) and t = time
  The total amount owing can then be calculated by adding I to P. That is,
  A = P + I.
• The following are the main formulas used in calculating simple interest, principal, time, rate and amount.
  
• If a principal P is invested at an annual rate of r, compounded annually, then the amount after t years is given by
  A = P(1 + r)^t.
• If a sum of money called principal P, is deposited in a bank, that pays an annual interest rate r compounded at a regular interval of time n times per year, the total accumulated amount A in t years is given by:
  
• If the rate of depreciation is r (as a decimal) per year and the present value of the asset is V, then the depreciated value, A, at the end of t years is given by
  A = V(1 - r)^t.