mathematics simple logic questions..for general knowledge

Order of Operations are:
* Parentheses (Brackets) first 
* Exponents (Orders, Powers, Square Roots, etc.) next
* Multiplication and Division (left-to-right) next
* Addition and Subtraction (left-to-right) last

So we do the division and multiplication before the addition and subtraction.

Multiplication and division rank equally and are done left-to-right:
5 × 3 - 12 ÷ 4 + 8
= 15 - 12 ÷ 4 + 8
= 15 - 3 + 8

Addition and subtraction rank equally and are done left-to-right:
15 - 3 + 8
= 12 + 8 
= 20