To cross multiply is to go
from this:
To
a × d = b × c
Table of Contents
How Does it Work?
Multiplying the top (numerator) and bottom (denominator) of a fraction by the same amount doesn’t change its value.
So, To cross multiply:
- Multiply the top and bottom of the left side fraction by the bottom number of the right side fraction.
- Multiply the top and bottom of the right side fraction by the bottom number that the left side fraction had.
- We can get rid of the b × d (as we are dividing both sides by the same amount) and the equation is still true
| Step 1 | Step 2 | Step 3 | |
|  |  | a × d = b × c |
Example
cross-multiplied form of
Is
4 × 14 = 7 × 8
Cross multiplication Application
Cross multiplication can help speed up a solution. Like in this
Examples
Find x in 
Cross Multiply:
x2 = 3 × 12 = 36
x = 6 or x = -6
Substitute both x values to the first form
We cannot use Cross Multiply when a denominator (b or d) is zero, as dividing by zero is undefined.