If grain prices double then the average price of a loaf of bread will rise between 10 and 15 percent, whereas the price of grain-fed beef will come close to doubling.
Given that ...
A doubling in the price of grain will only cause the average price of break to rise 10-15%
Why is it that ...
A doubling in the price of grain will cause the price of grain-fed beef to double?
Evaluate
We really could have framed this paradox either way, switching these two ingredients. We're really just trying to explain why a doubling in the price of grain would have a smaller effect on the price of bread than it would on the price of grain-fed beef.
Generally speaking, if you make a certain product, you have a lot of different expenses that go into setting your price. If one of those expenses (such as grain) were to rise by 30%, it wouldn't necessarily make the price of your product go up by 30%, because grain might be a very part of the expense to make your product.
For example, if strawberries rose in price, it might only modestly affect the price of a mixed berry yogurt, because there are other fruits in there as well, whereas it might more drastically affect the price of strawberry yogurt.
Goal
Look for an answer saying that grain is a more important ingredient / bigger category of expense when it comes to grain-fed beef than when it comes to a loaf of bread.