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Home > CC2 > Chapter 9 > Lesson 9.1.1 > Problem 9-10

9-10.
  1. Estimate the circumference or diameter for each of the following circles. For each one, give your reasoning. Homework Help ✎

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

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

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

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

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.

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

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.

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

The diameter is approximately 4 inches.