Pizza puzzle solved: 9-Inch vs. double 5-Inch, which one is worth it
Have you ever ordered a 9-inch pizza only to have the staff try to upsell you to two 5-inch pizzas with the line, 'You're actually getting an extra inch of pizza for free!'?
- A single 9-inch pizza offers significantly more food and better value than two 5-inch pizzas combined.
- The conclusion is based on the mathematical formula for the area of a circle (πr²), which shows the 9-inch pizza has a much larger surface area.
- The area of one 9-inch pizza is approximately 63.59 square inches, which is about 40% more than the combined 39.26 square inches of two 5-inch pizzas.
Have you ever ordered a 9-inch pizza only to have the staff try to upsell you to two 5-inch pizzas with the line, 'You're actually getting an extra inch of pizza for free!'?
Did you know that mathematics might offer a different answer? The Institute for the Promotion of Teaching Science and Technology (IPST) invites teachers, students, and the general public to join in a thought experiment: Which offers better value, one 9-inch pizza or two 5-inch pizzas?
You can find the answer and learn how to solve this using the mathematical concept of the "formula for the area of a circle" by watching the instructional video available on the Project 14 IPST online learning platform.
This is an online teaching project aimed at delivering Science, Mathematics, and Technology learning in video format, accessible anytime, anywhere.
Using the formula for the area of a circle (πr²), the IPST has revealed the definitive answer to the pizza value debate.
- π (Pi) is a mathematical constant with an approximate value of 3.14
- r (Radius): The distance from the centre of a circle to its edge.
- r² means r-squared, which is the radius multiplied by the radius, or r×r.
The Calculation Results
One 9-inch Pizza (r=4.5) 3.14×(4.5)² ≈ 63.59
Two 5-inch Pizzas (r=2.5) 2×[3.14×(2.5)² ] ≈ 39.26
The single 9-inch pizza provides significantly more food, boasting approximately 40% more area than the two 5-inch pizzas combined. This makes the 9-inch pizza the clear and definite winner in terms of value.
IPST emphasises that this engaging, real-world example proves mathematics isn't difficult or confined to books. Instead, it’s a vital tool that helps teachers, students, and the public "think critically, see connections, and make reasoned decisions" in everyday life.
You can find more fun, educational insights on the IPST Thailand Facebook page and access the free instructional video series on the Project 14 online learning platform anytime, anywhere.
