## 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.

An expression puts variables together with operators. For example, the expression for the area of a triangle is:
1                     b x h            where: b = base
--- x b x h   or      -------                  h = height
2                       2
Usually, multiplication of 2 variables is shown without any operator, like this:
bh       so, if  b = 5 and h = 4 then  bh =  5 x 4 = 20

Division is shown with a horizontal line, or a slash (/):
bh
----  =  bh/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 + 2x5 = 3 + 10 = 13 <= do the multiply first!

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

• ab = 3 x 5 = 15

•      5a     5x3     15
---- = ----- = ---- = 3
b      5       5