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?

   Hint (a):

   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 $\pi$, which is just over $3$.

   Answer (a):

   The circumference is $\pi$ cm, or just over $3$ cm.

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

   Hint (b):

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

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

   Hint (c):

   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?

   Hint (d):

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

   Answer (d):

   The diameter is approximately $4$ inches.