10. The formula for the circumference of a circle with diameter d is C = d. a. Solve the formula for d.
b. The circumference of a circle is 8 inches. What is the diameter of
the circle?
c. The circumference of a circle is 61 inches. What is the radius of
the circle?

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  a.  d = C/π

  b.  d = 8/π inches ≈ 2.546 inches

  c.  r = 61/(2π) inches ≈ 9.708 inches

Step-by-step explanation:

a. The formula for circumference is ...

  C = πd

Dividing by π gives ...

  d = C/π

__

b. For a circumference of 8 inches, the diameter is ...

  d = (8 in)/π = (8/π) in ≈ 2.546 in

__

c. The radius is 1/2 the diameter. So, the radius of a circle is ...

  r = d/2 = (C/π)/2 = C/(2π)

For a circumference of 61 inches, the radius is ...

  r = (61 in)/(2π) = 61/(2π) in ≈ 9.708 in

your answer would be 12