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Algebraic Proof Videos 8 videos

CAHSEE Math 5.1 Mathematical Reasoning
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Mathematical Reasoning Drill 5, Problem 1. Which of the following could be the number of pieces the lasagna was cut into?

CAHSEE Math 5.3 Mathematical Reasoning
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Mathematical Reasoning Drill 5 Problem 3. Which of the following could be the integer mentioned?

CAHSEE Math 5.5 Mathematical Reasoning
196 Views

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

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CAHSEE Math 5.5 Mathematical Reasoning 196 Views


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

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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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