Can YOU figure out which one is bigger – A 20-inch pizza or two 10-inch pizzas?

How do two pizzas with a diameter of 10 inches compare in size to one with a diameter of 20 inches?

If the 20-inch pizza was twice the price of a 10-inch pizza, would you be better off spending your money on two small pizzas or one large one?

Solution: 

Assuming the pizzas are perfectly circular disks and have the same uniform height, their volume can be calculated as follows:

The area of a circle is the radius (half the diameter) squared, multiplied by pi (3.14…).

The smaller 10-inch pie therefore has an area of:

5 inches x 5 inches x  ~3.14 = 78.5 square inches

Two 10-inch pizzas therefore have a total area of around 157 square inches

The larger 20-inch pie has an area of:

10 inches x 10 inches x ~3.14 = 314 square inches

Since 10 squared is 4 times larger than 5 squared, the area of the larger pizza is four times that of the smaller one.

The 20-inch pizza is therefore twice the size of the two 10-inch pizzas.

This can be visualized in a graphic that shows two smaller pizzas placed next to each other and on top of the larger one: