What is bid mas?

BIDMAS is an acronym used in the mathematics field to help remind people in what order a mathematical equation gets solved. The letters stand for

Brackets
Indices (squared, cubed, etc.)
Divide
Multiply
Add
Subtract

What you need to note though is that an equation is always solved from left to right. That is the #1 rule.

Second, you multiply and divide in the order they are written; same follows for addition and subtraction.

For example, 10+20*2/5 = 18
This is because you start by solving 20*2 = 40, then 40/5

If it were written 10+20/2*5 it would then equal 60. In this case you solve 20/2=10, then 10*5