Roxanne is measuring the diameter and the radius of different-sized circles.
There is a proportional relationship between the radius of the circle in inches, x, and the diameter of the circle in inches, y.
x (radius in inches) y (diameter in inches)
1 2
2 4
9 18
10 20
What is the constant of proportionality? Write your answer as a whole number or decimal.
inches in diameter per inch in radius