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CAHSEE Math 3.4 Mathematical Reasoning 180 Views


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Description:

CAHSEE Math: Mathematical Reasoning Drill 3, Problem 4. Which of the expressions gives the best estimate as to the length of this quadrilateral's perimeter?

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Transcript

00:03

Shmoop, there it is… Shmoop, there it is...

00:08

A quadrilateral has sides measuring 24.27 cm, 12.39 cm, 9.75 cm, and 25.99 cm.

00:18

Which of the following expressions gives the best estimate as to the length

00:21

of this quadrilateral's perimeter?

00:23

Here are the potential answers…

00:30

Ok, what is this question asking?

00:32

Well yeah, it’s testing our mad rounding skillz…

00:35

…but it’s also testing to make sure we can avoid traps.

00:39

We should note that our four answer choices apparently went to… 4 very different schools.

00:44

“A” rounds up or down to the nearest 10.

00:47

B SOMETIMES rounds up, sometimes down, sometimes to the nearest 1, sometimes to the nearest 10...

00:54

…and so on. They’re all over the map. In that case, we need to pay attention to

00:58

how far away we’re getting from the original number.

01:01

A goes down about 4, then down 2, the up almost nothin’, then up 4.

01:06

All told, A is only about 2 off the correct total. Not bad.

01:10

What about B? Down 4, down almost nothin’, up almost nothin’, and down 6.

01:16

Combined, off by 10 or so. No good. C is down 4, down 2, up almost nothin’,

01:22

up almost nothin’. Down 6 all day. A is still in the clubhouse with the lead…

01:27

Finally, D. Up 6, up almost nothin’, up almost nothin’, down 6.

01:32

There are some pretty big swings in there… but at the end of the day, it’s pretty spot on.

01:36

Our answer is D.

01:37

As in, “Duffer.”

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