# math

An apple pie 10 cm in diameter costs \$1.50. Then, an apple pie 20 cm in diameter should cost

a. \$3.00
b. \$4.00
c. \$4.50
d. \$6.00
e. \$8.00

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1. Those are awfully small apple pies.

Area = pi * r^2

A = 3.14 * 5^2
A = 78.5 square cm.

1.5 / 78.5 = \$0.019 per square cm

A = 3.14 * 10^2
A = 314 sq. cm

314 * 0.019 = \$5.97

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👩‍🏫
Ms. Sue
2. Since cost usually varies with the area

and the area is proportional to the square of the corresponding sides, the area would be 4 times as large, thus the cost would be 4(\$1.5) or \$6.00

( ratio of sides = 2:1
so ratio of areas = 2^2 : 1^2 = 4 : 1
ratio of costs = 4 : 1 )

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