Cambridge Primary Checkpoint 0845 · Topic 5 of 10

Ratio and proportion

Comparing amounts with ratios, sharing in a ratio, and solving problems where amounts are in direct proportion.

📌 Key points

A ratio compares one part with another part: 2 red beads for every 3 blue beads is red : blue = 2 : 3.
A proportion compares a part with the whole: 2 out of every 5 beads are red, so 25 of the beads are red.
Simplify a ratio by dividing both numbers by a common factor: 12 : 8 = 3 : 2.
The order matters: if boys : girls = 3 : 4, then girls : boys = 4 : 3.
To share in a ratio, add the parts, find the value of one part, then multiply.
In direct proportion, when one amount doubles, the other doubles too: 3 pens cost $6, so 6 pens cost $12.
The unitary method finds the value of one first: 4 kg cost $10, so 1 kg costs $2.50 and 7 kg cost $17.50.
Recipes use proportion: if 4 people need 200 g of flour, then 6 people need 300 g.

Ratio: A way to compare two or more amounts, written with a colon, e.g. 3 : 5.
Proportion: A part compared with the whole, often written as a fraction or a percentage.
Direct proportion: When two amounts go up or down at the same rate.
Simplify: To write a ratio or fraction with smaller numbers by dividing by a common factor.
Unitary method: Finding the value of one item first, then multiplying to find any number of items.

Sami and Lara share 35 sweets in the ratio 2 : 5. How many sweets does each of them get?

💡 Test tip

In sharing questions, add the parts of the ratio first, and check that your answers add up to the total.

Test yourself8 questions from a bank of 22. A new mix every time.