Question

Circle A has a diameter of 9 inches, a circumference of 28.26 inches, and an area of 63.585 square inches. The diameter of circle B is 5 inches, the circumference is 15.70 inches, and the area is 19.625 square inches..
Part A: Using the formula for circumference, solve for the value of pi for each circle.
Part B: Use the formula for area and solve for the value of pi for each circle.
Part C: What observation can you make about the value of pi for circles A and B?

Answer 1

Please note that pi has just one value.  The only difference stems from round-off error when you don't use all of the digits following "3.14159 ... " to represent the value of pi.  The formula for circumference is C = 2 pi r, or C = pi d, 
where r=radius and d=diameter.

Circle A:  Diameter 9 inches and Circumference of 28.26 inches

If the diameter is 9 inches, then C = 28.26 inches = pi (9 inches).  Divide 28.26 inches by 9 inches.  Note that you MUST round off the ratio (pi) that you obtain, since 28.26 has 4 significant figures and 9 has just one.

28.26
------- = 3.14, but because 9 has just one significant figure, you must round 
    9           this 3.14 to just 3.