Lesson 12
Exploring Circumference
Let’s explore the circumference of circles.
Problem 1
Diego measured the diameter and circumference of several circular objects and recorded his measurements in the table.
object  diameter (cm)  circumference (cm) 

half dollar coin  3  10 
flying disc  23  28 
jar lid  8  25 
flower pot  15  48 
One of his measurements is inaccurate. Which measurement is it? Explain how you know.
Problem 2
Complete the table. Use one of the approximate values for \(\pi\) discussed in class (for example 3.14, \(\frac{22}{7}\), 3.1416). Explain or show your reasoning.
object  diameter  circumference 

hula hoop  35 in  
circular pond  556 ft  
magnifying glass  5.2 cm  
car tire  71.6 in 
Problem 3
\(A\) is the center of the circle, and the length of \(CD\) is 15 centimeters.
 Name a segment that is a radius. How long is it?
 Name a segment that is a diameter. How long is it?
Problem 4

Consider the equation \(y=1.5x +2\). Find four pairs of \(x\) and \(y\) values that make the equation true. Plot the points \((x, y)\) on the coordinate plane.
 Based on the graph, can this be a proportional relationship? Why or why not?