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CAHSEE Math 1.3 Mathematical Reasoning 183 Views
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Description:
CAHSEE Math Mathematical Reasoning: Drill 1 Problem 3. Which of the following is the correct order of steps?
Transcript
- 00:03
You look too happy. Here’s an unshmoopy question to take you down a peg…
- 00:08
When solving the equation one over x minus one-half equals 3 for x,
- 00:13
which of the following is the correct order of steps?
- 00:16
And here are the potential answers...
- 00:20
OK, so this question is just pushing us to think about patterns of problem solving…
Full Transcript
- 00:25
and it throws in some curves and freebies as well.
- 00:29
Note that potential answer B asks about SUBTRACTING a half from both sides – well, since our
- 00:35
one-half on the left is already negative, we wouldn’t be able to cancel it out.
- 00:40
It would just be useless so we can eliminate option B right away.
- 00:43
Consider just the remaining 3 – and remember that the key goal in solving any of these
- 00:47
kinds of problems is to isolate x.
- 00:50
If we add a half to both sides – which is the first thing we do in the other potential
- 00:54
answers – the new equation looks like this:
- 00:57
1 over x equals 3 plus one-half.
- 01:01
So the next step is to just simplify 3 PLUS 1 half to be uh, yeah – 3 and a half.
- 01:08
Note that C has you subtracting a half as the second step here – and that’s just wrong –
- 01:13
we’ve ADDED a half to both sides; so you can cross out C.
- 01:17
So it gets down to D versus A.
- 01:21
A suggests taking the RECIPROCAL of the result whereas D asks us to take the OPPOSITE of the result.
- 01:28
The… opposite of the result? Not even sure what that would be. Sounds like someone who
- 01:32
just landed on our planet and is trying to fit in.
- 01:35
Taking the RECIPROCAL, however, makes sense.
- 01:37
Since we have 1 over x on the left side of the equation,
- 01:40
we can simply flip both sides to get x on the left…
- 01:44
…and one over 3 and a half on the right… which is 1 over 7 halves… or two-sevenths.
- 01:50
A it is.
- 01:51
As in… “Alien mathletes.”
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