Highest Common Factor and Lowest Common Multiple

In this activity, you will need to be able to find a common denominator and simplify 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 (numerator) and bottom (denominator) of  by 5.

This equals 

 

Simplifying a Fraction

We can simplify this fraction by dividing the numerator and the denominator by the same number.

 

We want to simplify a fraction to its lowest terms, so we divide the numerator and the denominator 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.