Maths GCSE Revision #9 – Finding a Fraction of a Number

Maths GCSE Revision - Lesson #9 – Finding a Fraction of a Number

This lesson from the ‘Number’ section of GCSE Maths is all about finding a fraction of a number, and writing different proportions as fractions. We have a look at a couple of examples first, before going on to a practice exam question (transcript below video).


Next up, we are going to look at how to find a fraction of a total amount. Here we are trying to find 4/5 of £220. This is our method, which involves two steps:

First, multiply the numerator by the total amount: 4 x £220 = £880.

Next, we divide this new amount by our denominator: £880 divided by 5 = £176.

So our final answer for this example, is £176. These are the two steps that you always want to follow in questions of this type.

Now we are going to look at how to write a proportion as a fraction. For example, writing 12 as a fraction of 72. For this example, our method is as follows:

Write your first number (12) as your numerator, and take your second number (72) as your denominator. This gives us a fraction of 12/72. Our last step is to simplify this fraction (which we looked at in lesson #6). Here, we can divide both parts of our fraction by 12 (giving us 1 and 6 respectively). So our fraction simplifies to:

12/72 = 1/6.

The last part of this video is a practice exam question involving the calculation of fractions of total amounts.

Exam Question 1: Write 180g as a fraction of 3kg. Give your answer in its simplest form.

In question 1, we are dealing with units (grams and kilograms), which we will look at in more detail in a later lesson. For now, we just need to make sure we write both of our values in the same units, which can be grams.

3kg = 3000g.

Now we can follow the same method as in the previous section. 180g will be our numerator, and 3000g will be our denominator. We can then simplify our fraction as much as possible, by dividing both numbers by common factors.

180/3000 = 18/300 = 6/100 = 3/50

Here, we have divided by the following numbers consecutively to simplify our fraction; 10, 3 and 2. Alternatively, you could have simplified your fraction in one step, by dividing both your numerator and denominator by 60.

Exam Question 2: Work out 2/3 of 36.

In question 2, we want to multiply our numerator by our total amount:

2 x 36 = 72.

Next, divide this new value (72) by the denominator in the question (3):

72 / 3 = 24.

So our final answer for question 2, is 24.


Thanks for watching, and if you have any questions about the topics talked about, or you are stuck on a particular concept, just get in touch and we will get back to you as soon as possible!