Proportional relationships: A relationship between two equal ratios.

Proportions are the comparison of two equal ratios. Therefore, proportional relationships are relationships between two equal ratios. For example, oranges are sold in a bag of 5 for $2. The ratio of oranges to their cost is 5:2 or . If I bought 20 oranges, I could set up a proportion to determine my cost. One common way of solving a proportion is to use cross-products. This would give you the equation 2*20 = 5*x or 40 = 5*x. To solve this, divide both sides by 5 to see that x = 8.
You can also solve this by figuring out how many bags of 5 you need to have 20 oranges. You would need 4 bags of 5 oranges to equal 20. Therefore, you would multiply $2 times 4 to get $8.