### Home > MC1 > Chapter 9 > Lesson 9.2.5 > Problem9-110

9-110.

Estimate the circumference or diameter for each of the following circles. For each one, give your reasoning.

1. The diameter is $1$ cm. What is the circumference?

The circumference of a circle can be thought of as the length of a string that wraps exactly around it once.
You can calculate the circumference by multiplying the diameter by $π$, which is just over $3$.

The circumference is $π$ cm, or just over $3$ cm.

2. The diameter is $7.2$ meters. What is the circumference?

What length is just over $3$ times longer than $7.2$ meters?

3. The circumference is $1$ mile. What is the diameter?

Since the circumference is just over $3$ times the diameter, it makes sense that the diameter is about one third the length of the circumference.

4. The circumference is $12$ inches. What is the diameter?

Use the same hint as in part (c), approximate your answer by substituting $3$ for $π$ once again.

The diameter is approximately $4$ inches.