Question

1. the radius of a circle is 10 in. find its circumference in terms of π.
2. the diameter of a circle is 18 m. find its circumference in terms of π.
3. the diameter of a circle is 20 m. find its circumference in terms of π.
4. the radius of a circle is 19 ft. find its circumference in terms of π.

Explanation:

Step1: Recall the circumference formula

The formula for the circumference of a circle is $C = 2\pi r=\pi d$, where $r$ is the radius and $d$ is the diameter.

Step2: Solve problem 3

Given $r = 10$ in. Using $C = 2\pi r$, we substitute $r = 10$ into the formula. So $C=2\pi\times10 = 20\pi$ in.

Step3: Solve problem 4

Given $d = 18$ m. Using $C=\pi d$, we substitute $d = 18$ into the formula. So $C = 18\pi$ m.

Step4: Solve problem 7

Given $d = 20$ m. Using $C=\pi d$, we substitute $d = 20$ into the formula. So $C=20\pi$ m.

Step5: Solve problem 8

Given $r = 19$ ft. Using $C = 2\pi r$, we substitute $r = 19$ into the formula. So $C=2\pi\times19=38\pi$ ft.

Answer:

Problem 3: $20\pi$ in.
Problem 4: $18\pi$ m.
Problem 7: $20\pi$ m.
Problem 8: $38\pi$ ft.