What is a proportion?

A proportion is two ratios that are equivalent (or equal).

Explain why the ratios 3 apples / 4 oranges and 6 apples / 8 oranges form a proportion.

The ratios form a proportion because they are equivalent; 6 apples / 8 oranges simplifies to 3 apples / 4 oranges.

No, it is not a proportion because the ratios are not equivalent. 4/1 is not equal to 8/3.

I can define "proportion" and identify the proportion that represents a proportional relationship.

1
A proportion is two equivalent ratios that are set equal to each other.
2
In order for two ratios to be equivalent, they must have the same value and the same units.
3
If three of the values in a proportion are known, you can use cross-multiplication to solve for the unknown value.