Posted by robert on .
A ball rolls along a circle whose radius is 2 ft. How far does the ball roll if it goes around the circle 12.5 times?
I got 25 ft as my answer. I just multiplied the two numbers and I got 25. Is this right?

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bobpursley,
Nope. The distance around the circle is PI*4.
PI*4*12.5= ? way over 25. Way over 100, but not over 200 
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robert,
is it 157.1?

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Ms. Sue,
I got 157 feet.

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robert,
how did you get that?

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Ms. Sue,
Using Bobpursley's formula of PI*4*12.5 =
3.14 * 4 * 12.5 = 157 
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Ms. Sue,
Oops. I assume the ball is rolling around the circumference of the circle, not the radius.
To find the circumference of the circle, use this formula, in which C = circumference, r = radius, and pi  3.14
C = 2r * pi
C = 4 * 3.14
C = ?
Now multiply 12.5 by the circumference.
If you post your answer we'll check it. You can also study about the circumference at this site.
http://www.mathgoodies.com/lessons/vol2/circumference.html