Variables, Operators and Expressions
A variable is a letter that stands for a number.  For example,
when
we used the letter "b" to stand for the base of a triangle, we were
using the variable b

An operator is add, subtract, multiply or divide.

Note: There are other operators but we won't go into them now.

An expression puts variables together with constants and operators. 
For example,
the expression for the area of a triangle is:
½ x b x h or 
(b x h) / 2 or 
(b x h)
2 
where: b = base and h = height

Usually, multiplication of 2 variables is shown without any
operator, like this:
b h so, if b = 5 and h = 4 then b h = 5 x 4 = 20
Division is shown with a horizontal line, or a slash (/) or the divide symbol (÷):
b h = b h / 2 = b h ÷ 2
2
So... if you have 2 variables "a" and "b", then...
If a = 3 and b = 5, here are some expressions:
a + b = 3 + 5 = 8 

a + 2b = 3 + 2 x 5 = 3 + 10 = 13 <= do the multiply first! 
ab = 3 x 5 = 15 

a  b = 3  5 =  2 <= Remember your negative numbers!

5a = 5 x 3 = 15 = 3
b 5 5 

Now, here is a problem for you:
If a = 7 and b = 5, what is
(8a  2b) / 2 = ______________


