Highest Common Factor and Lowest Common Multiple

In this activity, you will need to be able to find a common denominator and reduce a fraction in order to solve a range of questions.

 

Finding a common denominator

The lowest common denominator is the smallest number that is exactly divisible by each denominator of a set of fractions.

Sometimes when we have to add two fractions, we cannot do it because the denominators are different, both the denominators need to be the same.

 

 

To find the lowest common denominator, we see if the larger denominator (20) can be divided by the smaller denominator (4).

20 ÷ 4 = 5.

 

Therefore we multiply the top and bottom of  by 5.

This equals 

 

Reducing a Fraction

We can reduce this fraction and make it simpler by dividing the top and the bottom of the fraction by the same number.

 

We want to reduce a fraction to its lowest terms so we divide the top and the bottom number by their highest common factor.

 

The highest number that goes into 8 and 20 is 4.

 

8 ÷ 4 = 2

20 ÷ 4 = 5

Therefore 

 

Over to you now to use this knowledge to solve a range of different questions.