Predicting the Circumference

The class took the graph and put a line in, like this.

Then they chose two points on or near the line (3,10) and (13,40) and used them to determine a line. The slope was (40-10)/(13-3)= 3.0 and the intercept was 0.

The equation of their line was Y = 3X.
In other words the circumference = 3 times the diameter.< P> From geometry we know that the circumference = pi times the diameter, but pi is approximately 3.1416.
So their guess of 3 isn't so bad, what did you get?

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