ShmoopTube

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And here's your shmoop du jour...

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Cheryl is just learning to ride a bike. She’s nervous, and wants to start small.

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REALLY small. Her bicycle wheel has a diameter of 18.1 inches.

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Using the formula for the circumference of a circle, 

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C = πd, where d is the diameter, and C is the circumference…

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…she estimates that, with one full revolution of the wheel… which is as far as she wants to go…

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she travels a distance of about 54 inches, or 4.5 feet.

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Because of the way she made her estimation, her estimate will be... what?

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And here are the potential answers...

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OK, so this question is asking us about estimation, and how exact Cheryl's estimation is compared

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to the exact distance.

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We estimate all the time...what score we're going to get on the next math test…

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…how many marshmallows we can fit in our mouths, and so on.

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Using the circumference formula, C equals pi times diameter…

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…Cheryl must have rounded down the value of π to 3 and 18.1 to 18…

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…so then we just arrive at the value of C = 3 times 18 which is 54.

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Because she rounded down for both pi and the diameter, the product or circumference will

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be an underestimate of the exact distance.

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Answer is A.

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