FORMULA: Circle Area



FORMULA: Circle Area problems

1. Your favorite pizza place sells a small round 10 inch pizza for $6 and a round large 16 inch pizza for $12. Which deal gives more pizza for each dollar spent?

Show all work and, if necessary, round answers to the hundredths place.

2. First we need the formula for Area of a Circle: A = ( r2, or A = ( x r x r

where A = area, ( = pi = 3.14, and r = radius = ½ of the diameter

(Remember that diameter is measured all the way across the circle.)

Example: If d=8, ½ d = ½ x 8 = r = 4, so A = (x4x4 = 16( = 16 x 3.14 = 50.24

3. First find the small pizza area. Remember, r is ½ of the diameter, which is 10 in. Also, always show units. The units here are square inches, or sq in, or in2.

4. Now divide the answer from #3 by the price of a small pizza, which is $6. Units are in2 / $1.

5. Next find the area of the large pizza, which has a diameter of 16 inches. Units are in2 .

6. Now divide answer from #5 by the price of a large pizza, which is $12. Units are in2 / $1.

7. Compare the answers from #4 and #6. Which answer is larger? That is the one that gives you more pizza for every dollar that you spend.

8. What if you decided to buy two small pizzas instead of one large pizza? Which deal gives you more pizza to eat for $12? Take answer #3 and multiply it by two. Compare this new answer to the answer from #5. Which is larger?

9. Summarize in a paragraph what you learned from the answers in #7 and #8.

10. Describe a time when you would still rather buy 2 smalls than 1 large pizza.

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