Concept

Unlike fractions are fractions with different denominators. 

A fraction is said to be in the simplest form if its numerator and denominator have no common factors other than 1.

Rule

To subtract fractions with unlike denominators using models,
1. Find an equivalent fraction with a common denominator. The common denominator can be found by visually comparing the models.
2. Simplify, if needed, by dividing the numerator and the denominator by their greatest common factor. 

Example

Subtract. 

Write in the simplest form. 

Solution

1. If the denominators are not the same, find an equivalent fraction with a common denominator. The common denominator can be found by visually comparing the models. 

These models show that 13 is the same as 26.
Rewrite 13 as 26 , and subtract 

56 - 46 = 16

2. 16 does not need to be simplified.

Answer: 16

Pre-requisite Skills

Equivalent Fractions (4.15.5)