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Microsoft Excel: Find the Area of a Circle

written by: Mr Excel•edited by: Michele McDonough•updated: 7/6/2011

Problem: You need to order pizza for the department staff meeting. The pizza joint has two deals. You can buy three Medium (12") pizzas for $15 or two Large (16") pizzas for $16. Which is the better deal?

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    Strategy: You will have to figure out the area of a 12" pizza vs. the area of a 16" pizza. The formula for the area of a circle is Pi times the square of the radius.

    The radius of a pizza is one-half the diameter. If you enter the diameter of the pizza in B2, the radius is =B2/2.

    Pi is a Greek letter that represents 3.141592654. Excel offers the PI function to return this number, as shown in Fig. 445. It is a lot easier to remember =PI() instead of 3.141592654. (Click any figure below for a larger view of that image.)

    1) Set up a worksheet. In cell B2, enter the diameter of the pizza.

    2) In cell C2, calculate the radius as =B2/2, as shown in Fig. 446.

    3) In cell D2, calculate the area of the pizza in square inches, using =PI()*C2^2, as shown in Fig. 447.

    4) In column E, enter the quantity of pizzas.

    5) Calculate the total square inches in column F using =E2*D2, as shown in Fig. 448.

    6) Enter the cost for the special in column G. In column H, calculate the pennies per square inch of pizza using =G2/F2, as shown in Fig. 449.

    Result: From a purely mathematical point of view, the special with two large pizzas is a slightly better deal, pricing the pizza at 3.98 cents per square inch.

    Additional Information: My seventh grade math teacher, Mr. Irwin, would like me to mention, for the sake of completeness, that the circumference of the pizza is Pi times the diameter. That would be =PI()*B2, as shown in Fig. 450.

    Summary: To calculate the area of a circle, use the PI function times the radius squared.

    Functions Discussed: =PI()

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    Images

    Fig. 445Fig. 446Fig. 447Fig. 448Fig. 449Fig. 450