Domino's pizza
Pizzas are (traditionally) circular, and the size of a pizza is described by stating its radius. A 10-inch pizza is a circular pizza with a radius of 10 inches.
Domino can eat a 12-inch pizza in 20 minutes. At the same rate, how long will it take Domino to eat an 18-inch pizza?
The answer is 45.
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5 solutions
Note that the time it takes to eat the pizza varies directly with the size. If we try to solve by diameter, however, our calculations will be incorrect, because the size of the pizza is the area, not the radius. Let's instead compare the square of 12 and 18, because that is how many pi there are in the area. Setting up the proportion 2 0 1 4 4 = x 3 2 4 and solving, we see that it takes 45 minutes.