Pizza Math

Pre-Algebra · Axiom Academy

LESSON Pizza Math: Finding the Best Deal Pizza is a circle, so its area grows with the square of the radius — which is why the bigger pie is almost always the better buy. Make the radius twice as big and the pizza does not hold twice as much — it holds four times as much. Area lives in two dimensions: it scales with the radius times the radius. Watch a small pie (radius 4 in) sit next to a pie with double the radius (radius 8 in), each tiled with 1-inch squares. Double the radius → 4× the area To turn "how big" into a number, we use the area of a circle. The menu gives the diameter (the width across), so first halve it to get the radius , then square the radius and multiply by . Watch the radius sweep around the 16-inch pie and the area fill in as the running total climbs. A 16-inch pizza is 16 in across, so in. r^2 = 8^2 = 64 . This is where the "growth in two dimensions" lives. r = 5 , so in² — barely a third of the big one. Would you rather have one 16-inch pizza or two 10-inch pizzas? Areas decide it: one 16-inch is in², while two 10-inch are in². The single big pie wins by about 44 square inches — roughly 28% more food . 3. The Real Test: Price ÷ Area "Cheaper" sticker price doesn't mean "more food per dollar." To compare fairly, divide each pizza's price by its area to get the cost per square inch — spreading the same dollars across more pizza. The pie with the smaller price-per-area is the genuine deal. Watch each price spread out over its pizza.

This is the written version of the interactive lesson above. See the full Pre-Algebra course.