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# Basic algebra...can you help with a simple rule?

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SVP
Joined: 30 Apr 2008
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Location: Oklahoma City
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Basic algebra...can you help with a simple rule? [#permalink]

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09 May 2008, 09:50
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

ok, I have this question that I thought I had the answer to, but the "answer" is something different. Check out the stem:

If a = 3 and b = -2, what is the value of $$a^2 + 3ab - b^2$$?

This should be easy, and the hangup I have is on the $$-b^2$$.

I have set it up this way via substitution:

$$(3)^2 + 3(3)(-2)-(-2)^2$$

It appears to me the answer would be a -13.

The above becomes this:

$$9 -18 - 4 = -13$$

Am I correct in doing the square of the -2 first, so then you have - 4 (that's minus 4, or minus a positive 4, not negative 4)?

The answer is supposedly 5, which would mean the $$-(-2)^2$$ would have flipped the sign of -2 to a +2 and then squared that, for a + 4.

What is the correct order to do this in? I thought exponents came before addition/substraction?

Jarod
_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$. GMAT Club Premium Membership - big benefits and savings VP Joined: 10 Jun 2007 Posts: 1459 Followers: 7 Kudos [?]: 251 [0], given: 0 Re: Basic algebra...can you help with a simple rule? [#permalink] ### Show Tags 09 May 2008, 11:16 jallenmorris wrote: ok, I have this question that I thought I had the answer to, but the "answer" is something different. Check out the stem: If a = 3 and b = -2, what is the value of $$a^2 + 3ab - b^2$$? This should be easy, and the hangup I have is on the $$-b^2$$. I have set it up this way via substitution: $$(3)^2 + 3(3)(-2)-(-2)^2$$ It appears to me the answer would be a -13. The above becomes this: $$9 -18 - 4 = -13$$ Am I correct in doing the square of the -2 first, so then you have - 4 (that's minus 4, or minus a positive 4, not negative 4)? The answer is supposedly 5, which would mean the $$-(-2)^2$$ would have flipped the sign of -2 to a +2 and then squared that, for a + 4. What is the correct order to do this in? I thought exponents came before addition/substraction? Jarod You did it correctly. Exponent comes before add/subtract...Do you have the while question? CEO Joined: 29 Mar 2007 Posts: 2583 Followers: 19 Kudos [?]: 409 [0], given: 0 Re: Basic algebra...can you help with a simple rule? [#permalink] ### Show Tags 09 May 2008, 11:25 jallenmorris wrote: ok, I have this question that I thought I had the answer to, but the "answer" is something different. Check out the stem: If a = 3 and b = -2, what is the value of $$a^2 + 3ab - b^2$$? This should be easy, and the hangup I have is on the $$-b^2$$. I have set it up this way via substitution: $$(3)^2 + 3(3)(-2)-(-2)^2$$ It appears to me the answer would be a -13. The above becomes this: $$9 -18 - 4 = -13$$ Am I correct in doing the square of the -2 first, so then you have - 4 (that's minus 4, or minus a positive 4, not negative 4)? The answer is supposedly 5, which would mean the $$-(-2)^2$$ would have flipped the sign of -2 to a +2 and then squared that, for a + 4. What is the correct order to do this in? I thought exponents came before addition/substraction? Jarod Ya its -13, ur question is bugged. SVP Joined: 30 Apr 2008 Posts: 1887 Location: Oklahoma City Schools: Hard Knocks Followers: 40 Kudos [?]: 564 [0], given: 32 Re: Basic algebra...can you help with a simple rule? [#permalink] ### Show Tags 09 May 2008, 11:30 Thanks. That question was starting to make me question myself. That was the 2nd bug I'd found in 15 questions. I threw out the entire packet. I'm don't remember where I downloaded the practice test from, but it's obviously not worth much. Thanks. Jarod Any of you used an MBA Admissions consultant? If so, are they worth it? _________________ ------------------------------------ J Allen Morris **I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

GMAT Club Premium Membership - big benefits and savings

SVP
Joined: 30 Apr 2008
Posts: 1887
Location: Oklahoma City
Schools: Hard Knocks
Followers: 40

Kudos [?]: 564 [0], given: 32

Re: Basic algebra...can you help with a simple rule? [#permalink]

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09 May 2008, 11:36
Here's a great one from this same practice exam.

#7. Solve: 0.25 x 0.03 =

This one is so freaking simple, it's shocking they got it wrong. 25 x 3 = 75, and there are 4 digits right of the decimal, so the answer is 0.0075. Not according to this exam. It's 0.075. Here is their explanation for the answer:

"The number of decimal places to the right of the decimal poitn in the product will be the combined number of decimal places to the right of the decimal point in the two factors. In this case, the ten-thousandth lace is a zero and can be omitted."

I kid you not, that is the actual explanation for it. If I remember where I downloaded this thing I'll post it.
_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a.

GMAT Club Premium Membership - big benefits and savings

Intern
Joined: 09 May 2008
Posts: 2
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Kudos [?]: 0 [0], given: 0

Re: Basic algebra...can you help with a simple rule? [#permalink]

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10 May 2008, 00:53
I tried to solve my doubts at ***.com...I think everyone can benefit from that site..as i have benefited from this site im sure you will also...do check it out...

Last edited by chat on 28 May 2008, 07:38, edited 2 times in total.
Intern
Joined: 10 May 2008
Posts: 5
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Re: Basic algebra...can you help with a simple rule? [#permalink]

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10 May 2008, 01:26
Yeah....*** is a good site...really helps with the videos and all...great work....
Re: Basic algebra...can you help with a simple rule?   [#permalink] 10 May 2008, 01:26
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