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CAHSEE Math Videos 210 videos
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CAHSEE Math 4.4 Number Sense 195 Views
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Description:
Number Sense: Drill Set 4, Problem 4. Solve the expression.
Transcript
- 00:03
Here's your shmoop du jour.
- 00:06
2/5 divided by... 1/15 minus 3/10 equals...what?
- 00:12
And here are the potential answers...
- 00:16
Well, this question isn't big on words -- it's just asking whether we can subtract and divide fractions.
- 00:21
Piece of cake. Because we don't want to make PEMDAS mad,
Full Transcript
- 00:24
we start with the junk inside the parentheses.
- 00:28
First we have to get a common denominator for 15 and 10.
- 00:34
Both fit into 30 pretty easily... in that case, let's multiply top and bottom of 1
- 00:38
over 15 by 2 to become 2 over 30...
- 00:43
...then we multiply top and bottom of 3 over 10 by 3 to get 9 over 30.
- 00:49
2 minus 9 is -7... so we can rewrite the problem now as 2 fifths divided by -7 over 30.
- 00:56
And remember that dividing by a fraction is the same thing as multiplying by its inverse.
- 01:01
So rewrite the problem as:
- 01:03
Two fifths TIMES -30 over 7
- 01:07
And we have -60 over 35
- 01:10
We can reduce that bad boy to -12 over 7 and voila -- it's answer A.
- 01:15
Thank goodness. Now we won't have to deal with the wrath of PEMDAS.
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