Ratio and proportion

Share an amount in a ratio, simplify a ratio and use the unitary method. About 9 minutes, KS3 / GCSE.

What you will do

1. What a ratio says. A ratio such as 3 : 4 compares parts. It does not say how big each part is, only how they relate: for every 3 of the first there are 4 of the second.
2. Sharing in a ratio. Add up the parts, divide the amount by that total to find one part, then multiply.
3. Simplifying a ratio. Divide every part by the highest number that goes into all of them, just like simplifying a fraction.
4. Equal ratios. Two ratios are equal when they are the same fraction. Find the scale factor between them and apply it to the other part.
5. The unitary method. Find the value of one first, then scale up.