How can you use a rate to compare the costs of two boxes of cereal that are different sizes?

We can find the Unit Price of the box.
Both boxes will have the mass and price printed on them.
Suppose firat box if of 2 kilogram and costs $10.
While second box is of 5 kilogram and costs $25.
We can divide the price by mass and find the unit price.
So
Unit price = 25/5 = $5 per kilogram
Similarly
The other one also gives the same answer
10/2 = $5 per kilogram

This is how we can compare the prices using unit rates.

b.an increase in a causes b to decrease

goog may be able to you find that answer