The term direct proportion means that two (or more) quantities increase or decrease in the same ratio. In our previous paint example we could use direct proportion to mix enough paint to decorate just one wall, or enough to paint one room, or enough to paint an entire apartment block; if the ratio remains the same, the mixture of paint will remain the same color.
Direct Proportion Examples
Here are some more examples of the types of problems that can be solved using direct proportion.
Ratio of pizza to people is 1:3
|12 ÷ 3 = 4 |
In the following examples we will ask ourselves, "how much for one?" Problems with ratio and proportion can often be solved using this strategy.
Ratio of people to beef is 5 people : 10oz.
|10 ÷ 5 = 2 |
|2 x 8 = 16 |
How much fertilizer?
Ratio of fertilizer to area is 20 lbs : 1,000 sq. ft.
|20 ÷ 1,000 = .02 |
|.02 x 700 = 14 |
|Since we are dealing with bigger numbers we could also solve this problem by asking "how much for 100 sq. ft." |
20 ÷ 10 = 2
|2 x 7 = 14 |
Try this Proportional Ratios worksheet
You will find other worksheets on ratio and proportion here.