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Highest Common Factor, Lowest Common Multiple: Probing Questions

Whether you are looking for a question to stimulate discussion in lesson, or a challenge at the end of a homework, then hopefully you will find these useful.

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Convince Me That... keyboard_arrow_up
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I use Convince Me That questions lots in my lessons and homeworks. Providing students with a statement and challenging them to come up with as many different ways of convincing you as possible can lead to some fascinating discussions. The different ways of seeing the same thing can also help improve the depth of students’ understanding. Thanks so much to the Thornleigh Maths Department, in particular Erica Richards, Anton Lewis and Gareth Fairclough for helping me put these together, and we will endeavour to keep adding more!

1 must be the highest common factor of 7 and 37.

Multiplying two numbers together does not always give the lowest common multiple.

You can find the highest common factor and lowest common multiple of two numbers when the product of prime factors is expressed in a Venn Diagram

Different pairs of numbers can have the same LCM/HCF

VI3 Treatment keyboard_arrow_up
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We devised VI3 Treatment as a versatile way of giving students meaningful follow-up work at once we have marked their homework. The idea is that students are challenged to come up with 3 things with certain constraints. These are ideal to use as an extension for students who have got everything correct, and also as further purposeful practise for students who have got a particular question wrong. Use the ideas below and adapt them accordingly, using different numbers where appropriate. Either mark them yourself or better still, get other students to do it. Thanks so much to the Thornleigh Maths Department, in particular Erica Richards, Anton Lewis and Gareth Fairclough for helping me put these together, and we will endeavour to keep adding more!

Find 3 pairs of numbers which have a highest common factor of 6.

Find 3 pairs of numbers which have a lowest common multiple of 30

Find 3 pairs of numbers which have no common factors other than 1, but are not prime numbers.

Find 3 different pairs of numbers that have the same highest common factor and the same lowest common multiple