I’ve got a small year 10 class that struggle with number work. We had good lesson looking at writing numbers as a product of prime factors, but they had a significant learning block in not being able to quickly find two factors of numbers when constructing their factor trees.
I’ve made the following multiplication table that is adapted specifically for writing numbers in prime factor form. Say pupils are trying to find two factors of 28, they find it in the grid then read up and across to find the two factors, 2 and 14 or 4 and 7 etc. They then continue constructing their factor trees with these new factors, using the grid to find two more etc.
Quite often pupils need to go beyond the 10 X 10 times tables in this task, for example spotting that 26 = 2 X 13, so I have extended one side of it up to 30. The primes are shaded and I have removed all the 1 X y where y is a composite number so they don’t start putting 1s and ys into their prime factor trees.
Using the grid effectively will certainly require some demonstrations first. I’m going to give it a go tomorrow and see how they get on. Ultimately it would be nice if it led to conversations about strategies for finding the factors without the grid, but that can be another lesson rather than trying to tackle both things at once…
Click here to download the product of prime factors multiplication grid
