Theory:

Mathematical expressions have to be reduced as per the BIDMAS rule.
 
Consider the expression 5+12÷3(87).
 
Here the confusion is how to start solving the expression. Whether to add \(5\) and \(12\) first, or divide \(12\) by \(3\) or subtract the numbers which are present inside the bracket.
 
To avoid this confusion, we have to use the BIDMAS rule.
 
The word BIDMAS stands for BRACKET, INDICES, DIVISION, MULTIPLICATION, ADDITION and SUBTRACTION.
  
LetterMeaningSymbol
BBrackets() or{} or []
IIndicespower of number(You will learn later)
DDivision÷
MMultiplication×
AAddition\(+\)
SSubtraction\(-\)
Example:
Try solving the following expression by BIDMAS rule.
 
5+12÷3(87)
 
Simplify the values in the brackets.
 
5+12÷31
 
As we don't have any indices do the division.
 
5+41
 
Now do the addition.
 
91
 
Now do the subtraction.
 
\(8\).