4 + 5 · 2^{ 3}.In this expression the numbers are 4, 5, 2 and 3 and they are combined by the operations of addition, multiplication and exponentiation.
3 (4 + 5) + 2.Here the subexpression is 4 + 5. A more complicated example is:
10 (3 (4 + 5) + 2)It is the previous expression multiplied by 10. This expression contains a subexpression which itself contains a subexpression! The question then arises: in what order do we carry out these operations? The answer is given in this table:
Order of operations:

Algebra Coach Exercises 
Algebra Coach Exercises 