A proportion looks like this:

It means that the quantity a,b,c and d are in the same proportion: the ratio between a and b is the same ratio between c and d.
They are particularly useful in situation when you have an example given, and you want to extrapolate the relationship for another couple.
For example, you can think of the following problem: "Five apples cost 2 dollars. How much will 8 apples cost?"
You can build the proportion

And then solve it for x:

Ratio is written in x:y. therefore for this case, red:yellow
5 : 7
since the question states that there are 392 yellow poms, the 7 units represents 392 yellow poms. now you have to gind what is one unit and then multiply by 5 to find the number of red poms.
392 represents 7 units
1 unit: 392/7=56
5 units: 5×56=280 red poms
therefore the answer is 280 red poms which is C.
Answer:
Step-by-step explanation:
1 × 99 = 99. 3 × 33 = 99. 9 × 11 = 99