1. Cross Multiplication.
4x + 16 = ……………..

2. Cross Multiplying Fractions.
Consider the fractions below:
To cross multiply we multiply across the equal sign as shown by the arrows:
3 x 8 =
4 x 6 24 = 24
Now try these ones yourself.
(1)
(3)
(2)
18 = 18
70 = 70
48 = 48

3. Equation Solving
We can now use the cross multiplication technique to solve equations.
Solve:
(1) Cross multiply the equation.
(2) Solve as normal. 8x =
4 x 6 24 x = 8
The answer is telling you that three quarters is the same as six eighths.
x = 3

4. Further Example. 6y 7 x 8 = y = 56 6 y = y = Solve :
(1) Cross multiply the y term first.
(2) Solve as normal. 6y
7 x 8 = y = 56 6 y = y =

5. What Goes in The Box ?
Solve the following equations using cross multiplication.
(1)
(4)
x = 2
(2)
(5)
w = 12
(3)
(6)
f = 14