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