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Factors and highest common factors
- Slides in PPTX (with click-to-reveal answers)
- Slides in PDF (one slide per page, suitable for importing into IWB software)
- Worksheet (with space for student work)
- Handout (slides with exercises only; 4 per page for reduced printing)
- An Abbott and Costello scene “showing” that 7 x 13 = 28 (external site)
We need to understand factors before we can understand prime numbers. Prime numbers are very interesting in their own right and underpin many areas of pure mathematics. They are also incredibly useful in the real world – prime numbers are used in cryptography – keeping information secure, for example on the internet.
Prime numbers also appear in the natural world. Cicadas are insects which spend most of their lives underground but appear above ground periodically. Most appear either every 13 or 17 years. Because these numbers have only two factors, only rarely will a predator species with a shorter life cycle be able to take advantage of the huge numbers of cicadas emerging when they do: