Answers:
The 12-inch pizza costs about 9 cents per square inch while the 18 inch pizza costs 8 cents per square inch. The larger pizza is a better deal.
Note: the "0.08 cents" should be "8 cents".
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Step-by-step explanation:
The 12 inch diameter divides in half to get a radius of 12/2 = 6 inches.
area = pi*(radius)^2
area = 3.14*(6)^2
area = 113.04
The 12-inch diameter pizza has an area of roughly 113.04 square inches. This value is approximate since pi = 3.14 is approximate.
Divide the cost over the area to get the cost per area. We can call this the unit cost.
Unit cost = (total cost)/(total area)
Unit cost = (10 dollars)/(113.04 square inches)
Unit cost = 0.08846 dollars per square inch
Multiply this with 100 to convert from dollars to cents. This is the same as moving the decimal point two spots to the right.
The 0.08846 dollars becomes 8.846 cents, which we can round to 9 cents per square inch when rounding to the nearest cent.
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The other pizza (the 18-inch diameter) has an area of roughly 3.14*9^2 = 254.34 square inches. The unit cost is
(20 dollars)/(254.34 sq in) = 0.07863 dollars per sq inch approximately
That converts to about 7.86 cents per square inch, which rounds to 8 cents per square inch.
Your teacher wrote "0.08 cents per square inch" when s/he should have said "8 cents per square inch". Or perhaps they meant to say "0.08 dollars per square inch".
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Summary:
- The smaller pizza (12-inch diameter) costs about 9 cents per square inch
- The larger pizza (18-inch diameter) costs about 8 cents per square inch
- The larger pizza is the slightly better deal.