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  a) 50π cm^2

  b) π/8

Step-by-step explanation:

a) The formula for the area of a semicircle is ...

  A = (1/2)πr^2 = (1/2)π(d/2)^2 = (π/8)d^2

For a diameter of 20 cm, the area is ...

  A = (π/8)(20 cm)^2 = 50π cm^2 . . . . . the area of the semicircle

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The formula for the area of a quarter circle is ...

  A = (1/4)πr^2

For a radius of 20 cm, the area is ...

  A = (π/4)(20 cm)^2 = 100π cm^2 . . . . . the area of the quarter circle

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The shaded area is the difference of the areas of the quarter circle and semicircle:

  shaded area = (100π cm^2) -(50π cm^2)

  shaded area = 50π cm^2

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b) The ratio of the shaded area to the square area is ...

  shaded area / square area = (50π cm^2)/(20 cm)^2 = π/8

45

step-by-step explanation:

2160ft3

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