Ratio Problems
Solve problems involving the relative sizes of two quantities where missing values can be found by using integer multiplication and division facts
What a learner can do afterwards
- If the ratio of red to blue beads is 3:5 and there are 15 blue beads, find the number of red beads
- Use multiplication facts to find the missing value: 'For every 2 apples there are 5 oranges; if there are 20 oranges, how many apples?'
- Explain the multiplicative relationship between two quantities in a ratio context
The lesson
You already know how to compare two amounts with a ratio, like 3:5. In a ratio problem, you are told one amount and asked to find the matching amount for the other side. The two amounts always scale up or down by the same multiplying number.
The ratio of red to blue beads is 3:5, and there are 15 blue beads. Blue went from 5 to 15, so it was multiplied by 3 (5 x 3 = 15). Red and blue always scale together, so multiply red by 3 too: 3 x 3 = 9. There are 9 red beads.
Find the multiplying number first. Divide the new amount by its matching ratio number, then multiply the other ratio number by that same amount.
To solve a ratio problem, work out how much one side was scaled, then scale the other side by the same amount.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.