Using comparison bar models across the curriculum
Comparison bar models work when there is a difference between amounts. You can apply them to different areas of maths, including money, time, and measurement.
Often you see vocabulary like:
- More than
- Less than/fewer than
- Heavier than
- Taller than
- Larger than
- Smaller than
- As many as
- As much as
Solving addition and subtraction problems
Comparison bar models are perfect for ‘how many more?’ and ‘how many fewer?’ questions. They tackle the misunderstanding that ‘fewer’ will always need subtraction and ‘more’ means add.
Introduce them to your class, start by talking about two different amounts.
Ask, “which has more, which has fewer?”
You can encourage learners to use different colours to draw their own bars on squared paper to represent the amounts. One bar will be shorter than the other. Then, it’s a simple step to ask how many more or fewer one bar has.
To help you get started, here are some example questions:
- I have 5 sweets. My sister has 4 more than me. How many does she have?
- I ran 7km on Saturday and 5km on Sunday. How many more kilometres did I run on Saturday? (In this question ‘more’ needs subtraction not addition)
- Billy has 25 marbles. Sally has 35 more than him. How many do they have in total?
- Alf, Bart, and Carina have some buttons. Alf and Bart have 185 buttons. Carina has 101 buttons. Alf and Bart give Carina the same number of buttons. They all now have the same amount. How many buttons did Alf give Carina?
- There were 24 fewer children than adults at a cinema. After 2/5 of the children and 2/3 of the adults left, there was the same number of children and adults at the cinema. How many people went to the cinema altogether?
As you can see, the questions grow in complexity. But bar models are there to help learners visualise the difference in amounts and find a starting point for calculating the solution.
Solving ratio problems
You don’t have to limit yourself to addition and subtraction. Comparison bar models can be great for ratio questions too:
- Ellie and Alisha have trading cards in the ratio of 2 to 3. They have 30 cards altogether. How many cards does Alisha have?
- I am making a necklace. I want 5 blue beads for every 3 yellow beads. If I’ve used 40 beads, how many were blue, and how many were yellow?
- I’m planting bulbs in my garden. I plant 3 daffodils for every 4 tulips. I’ve planted 60 daffodils. How many tulips have I planted?