This is a demonstration of how to find the highest common factor (HCF or GCD) and the lowest common multiple (LCM) of two numbers.
Before starting you need to know your times tables and the divisibility tests.
Example 1. Find the HCF and LCM of 72 and 96:
You can vary the speed using this slider:

HCF & LCM CalculatorTransum subscribers are able to choose their own numbers for this calculator. They are able to type their two numbers into a form which appears here and see the highest common factor and lowest common multiple being revealed above. The solutions to Transum puzzles, exercises and activities are also available when you are signed in to your Transum subscription account. If you do not yet have an account and you are a teacher, tutor or parent you can apply for one by completing the form on the Sign Up page. A Transum subscription also gives you access to the 'Class Admin' student management system, downloadable worksheets, many more teaching resources and opens up adfree access to the Transum website for you and your pupils. This method is sometimes known as the Indian Method Many people know the highest common factor as the greatest common divisor and use the abbreviation GCD instead of HCF. 

