At a pizzeria, a medium pizza which has diameter of 12 inches sells for $6.00 and a large pizza which has a diameter of 16 inches sells for $10.00. which pizza is the better deal because it costs less per square inch?

We are comparing areas, so square of the linear dimension
Relative cost per unit area
12^2/6=24
16^2/10=256/10=25.6
Since 24<25.6, the 12" pizza is a better deal.

Note: we could compare exact area by calculating A=pi (d^2)/4, but since it is a relative comparison, the result will be the same, albeit more work.