HCF and LCM
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 8 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Two buses, one stop
- The highest common factor
Read the transcript of the teaching part
Last time
Before we start: last time, in Primes, factors and prime factor trees, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Two buses, one stop
One bus leaves a stop every twelve minutes, another every fifteen. They leave together at nine o'clock. When do they next leave together? That is a lowest common multiple problem. Cutting things into equal pieces is a highest common factor problem. Today you learn both.
The highest common factor
The highest common factor of two numbers is the biggest number that divides into both. List the factors of eighteen: one, two, three, six, nine, eighteen. List the factors of thirty: one, two, three, five, six, ten, fifteen, thirty. The common ones are one, two, three and six. The highest is six, so the HCF is six.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Primes, factors, HCF and LCM.
The whole chapter: Numbers and the Four Operations.
Chapter 1: Number
- Number families, reciprocals and ordering 6 min
- The four operations and negative numbers 6 min
- Primes, factors and prime factor trees 6 min
- HCF and LCM 5 min
Also for IGCSE Maths 0580
Which topics come up most in IGCSE Maths 0580 past papers, counted from every paper since 2004.