Finding the **Highest Common Factor (HCF)** is an important topic in maths that is useful in a number of skills, including fractions, mental maths, problem solving and many more.

Sometimes the HCF is referred to as the **Greatest Common Factor (GCF)** too - these meanings are identical.

In this activity, we will learn about how to find the HCF using lists.

**What does HCF mean?**

A **factor** is a number that you can divide a target by without leaving a remainder.

**Common **means that it appears more than once.

So the **HCF** is just the **highest number that appears in the factor list for two (or more) numbers**.

**e.g. Find the HCF of 10 and 25.**

The first step for these questions is to write out a list of all the factors:

**10: **1,2,5,10

**25:** 1, 5, 25

From this, we can see that the largest number that appears in both lists is **5**.

So the **HCF of 10 and 25 is 5**.

In this activity, you will find the HCFs of number pairs by creating lists and finding the highest option which appears in both lists.

You may want to have a pen and paper handy so that you can write out your lists before selecting your answers.