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CAHSEE Math 5.5 Mathematical Reasoning 196 Views


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Description:

Mathematical Reasoning Drill 5, Problem 5. How many pencils could Mrs. Morrison have had?

Language:
English Language

Transcript

00:03

Here’s a question with a beat you can shmoop to…

00:06

Mrs. Morrison is all about technology.

00:09

Which is why she wants to replace all the pencils in her classroom with… mechanical pencils.

00:15

On the first day of class, she had planned to distribute the mechanical pencils to her 30 students.

00:20

She had figured that if every student received the same number of pencils,

00:23

there would be 5 pencils left over. Instead of handing out the pencils on the

00:28

first day, she decided to hold off until the size of her class had stabilized.

00:36

A few days later, when she actually distributed the pencils, there were 25 students and there

00:41

were still 5 pencils left after the equal distribution.

00:45

How many pencils could Mrs. Morrison have had?

00:48

And here are the potential answers...

00:52

OK, so this question is just asking us to plug

00:55

in the potential answers one by one and figure out the remainders.

01:01

We have to get a number such that the remainder is 5 after dividing by both 25 and by 30.

01:08

So… consider A. With 125 pencils and the 25 student alternative, there would be NO

01:13

pencils left over – so... we can reject A.

01:17

Consider B with 130 – in this case, we’d have remainders of 5 and 10 –

01:21

so, not 5 and 5 which is what we seek… so punt B.

01:26

Now C: 150. Well, 25 and 30 go into 150 evenly so there’d be NO pencils left for either solution.

01:35

Try D: 30 into 155 gives us 150 evenly with 5 leftover;

01:41

and 25 into 155 gives us 150 evenly with 5 leftover…

01:46

So the answer to this oddball question...

01:48

...and this strange woman Mrs. Morrison dot com...

01:51

...is D.

01:52

As in, “Don’t tell Mrs. Morrison dot com about computers.”

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