Proportion · Grade 6
In Grade 6 you learn: scaling recipes and the unitary method.
Two quantities are in direct proportion when they grow together at the same rate: twice as many tickets cost twice as much. In inverse proportion one goes up as the other goes down: twice as many workers take half the time. The unitary method — find the value of one — solves almost every proportion problem.
Key facts
- Unitary method: find the value for 1, then multiply up.
- Direct proportion: both quantities are multiplied by the same number.
- Exchange rates: multiply to change into the new currency; divide to change back.
- Recipes: work out the amount per person, then multiply by the number of people.
Worked examples
Example 1
5 notebooks cost $6.50. How much do 8 cost?
Answer: $10.40
Example 2
A pancake recipe for 4 people uses 120 g flour, 2 eggs and 300 ml milk. You have 500 g flour, 5 eggs and 1 liter of milk. What is the largest number of people you can serve?
Answer: 10 people