What is the diameter of a circle whose circumference equals 15 miles?

We know the equation to find the circumference is:

C = π * D

Where D is the diameter. We are given the circumference so replace C with that:

15 = π * D

Divide both sides by π to get D, diameter, by itself:

D = 15/π

Diameter ≈ 4.775 miles

15 = 2(3.14159)r
15 = 6.28318r
r = 2.387326

d = 2.387326 * 2
d = 4.774652

Answer: 4.774652 miles is the diameter.

Circumference Equals Diameter

C=2 pi r 15=2pi r 15/2pi=r r=2.38732 d=2r d=2(2.38732) d=4.77465

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RE:
What is the diameter of a circle whose circumference equals 15 miles?

I need to find the circumference of a circle whose diameter is equal 19?

c = πd
d = c/π
(diameter = circumference/pi)

15 miles/π
= 15 miles/3.14
= 4.777070063694... miles
≈ 4.777 miles

C = π d
π d = 15
d = 15 / π
d = 4.77 miles

Circumference = pi x diameter or pi x 2r (r = radius)
Area = pi r^2 (pi r squared)
Given C = 15 ... to solve for the diameter divide by pi
15 = (pi)D, D = 15/pi
4.77 = D, r= D/2, r = 2.39

A = pi r^2
pi (2.39)^2 =
pi (5.71) = 17.94

Geez, I just realized that you only asked for the diameter ... why did I think you wanted the area??
Anyway, now you have it!

C=2*pi*r

We know C is 15 and for pi I will use 3.14. We need to find 2*r or d the diameter.

15=3.14d

d=15/3.14

d=4.777070