Lesson 1. Ratio

We use ratio to compare parts of a whole.

It this diagram, there are 6 black squares and 2 white squares.

We say the ratio of black squares to white squares is 6 to 2.

This is written as 6:2.

Both numbers in the ratio 6:2 can be divided by 2 so we can reduce the ratio 6:2 to its simplest from of 3:1.

EXAMPLE:

In a class of 24 children, 14 are girls. Find the ratio of boys to girls. Give the answer in its simplest form.

There are 10 boys. Ratio of boys to girls = 10:14. (10 and 14 can both be divided by 2).

Ratio of boys to girls = 5:7.

EXAMPLE:

Are the ratios 15:25:30 the same as 3:5:6?

15, 25 and 30 can all be divided by 5.

15 ÷ 5 = 3

25 ÷ 5 = 5

30 ÷ 5 = 6

So 15:25:30 = 3:5:6. 

Tasks to the lesson 1

• Test 1
• Test 2
• Test 3

Other lessons:

• Lesson 3. Direct proportion
• Lesson 5. Sharing in a given ratio
• Lesson 6. Percentages
• Lesson 7. Percentage of a number
• Lesson 9. Percentage change
• Lesson 10. Compound interest-type problems
• Lesson 11. Tasks for a time