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

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SVP
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Basic algebra...can you help with a simple rule? [#permalink] New post 09 May 2008, 09:50
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
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J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a$$.

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Re: Basic algebra...can you help with a simple rule? [#permalink] New post 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? 8-)
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Re: Basic algebra...can you help with a simple rule? [#permalink] New post 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
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User avatar
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

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

Get the best GMAT Prep Resources with GMAT Club Premium Membership

SVP
SVP
User avatar
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

GMAT Tests User
Re: Basic algebra...can you help with a simple rule? [#permalink] New post 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.
_________________

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

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