Proportion
Ratio
noun, verbal noun
This is a tough one. When you compare examples (in this case of numbers) you are figuring out the proportion / ratio. A ratio, for example, has one number on top of another. They are examples being compared. Same with proportions. Without two things to compare, proportion doesn't make sense. That's why when you compare examples, you are dealing with proportions or ratios.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
それに比例して、コストも上がります。
Costs will also increase in proportion.
これがyの大きさに比例するのは分かりますか？
Do you see how this is proportional to the value of y?
ボクは、仕事の大変さと楽しさは比例すると思うんだ。
I think the enjoyment I get from work is proportional to how hard it is.
外国語能力は、学習時間に比例して高くなるというワケではない。
Foreign language proficiency doesn't necessarily improve in proportion to the amount of time spent studying.