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CAHSEE Math 3.5 Mathematical Reasoning 227 Views


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Description:

Mathematical Reasoning Drill 3, Problem 5. Because of the way Cheryl made her estimation, her estimate will be what?

Language:
English Language

Transcript

00:02

And here's your shmoop du jour...

00:04

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

00:08

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

00:13

Using the formula for the circumference of a circle, 

00:16

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

00:20

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

00:25

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

00:30

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

00:35

And here are the potential answers...

00:40

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

00:46

to the exact distance.

00:48

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

00:52

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

00:55

Using the circumference formula, C equals pi times diameter…

01:00

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

01:07

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

01:14

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

01:18

be an underestimate of the exact distance.

01:21

Answer is A.

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