B O D M A S means as under. This is used when we simplify the expressions.
B = Brackets
O = Of
D = Division
M = Multiplication
A = Addition
S = Subtraction
When an expression is to be simplified, first we have to remove the Brackets.
By simplifying the expression within the brackets, then secondly Of means we have to do the operations like 1/4th of or 20% of etc.
Then we have to do the Divisions in the expression.
Then we have to do the Multiplications in that expression
Then we have to do the Additions and Subtractions in the last to arrive at the correct answer. So to remember which to do first and which then, we have to remember the word BODMAS.