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Possible error on OG GMAT 2017

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pilotmike327
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Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 16:03
Not sure if this is the right place to ask. On page 48 for the step-by-step solution for question 8, underneath the portion of the explanation where it shows the formula average=sum of values/ number of values, it starts with 2/5d + 2/10d divided by 2. Shouldnt it be 1/10d instead of 2/10d?
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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 17:20
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pilotmike327 wrote:
Not sure if this is the right place to ask. On page 48 for the step-by-step solution for question 8, underneath the portion of the explanation where it shows the formula average=sum of values/ number of values, it starts with 2/5d + 2/10d divided by 2. Shouldnt it be 1/10d instead of 2/10d?

Dear pilotmike327,
I'm happy to respond. :-)

Yes, it is a bit tricky to know where to ask about a possible typo in the OG: this sub-forum is as good a place as any.

I am sitting here with the OG2017 open, and on p. 48, I see

\(j = \frac{1}{2}(\frac{2}{5}d) = \frac{1}{10}d\)

In other words, I see the correct math, not the typo you describe. This problem is from the Diagnostic Test, which has remained unchanged through several successive editions of the OG. Take a look at the page again. I believe everything is error free.

Mike :-)
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pilotmike327
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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 17:48
I see that part is correct on my end as well but I am referencing the equation right before the paragraph that states: Solve for the store's revenue in December by multiplying both sides of this equation by 4.

The full average explanation shows:
average =2/5d + 2/10d divided by 2 = 4/10d + 1/10d divided by 2 = 5/10d divided by 2 = 1/2d times 1/2 =1/4d.
i am just curious why the equation starts with 2/5d +2/10d divided by 2 and not 2/5d + 1/10d divided by 2.

Btw, just signed up for Magoosh yesterday. Loving it so far!
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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 18:21
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Here is the page for reference.


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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 18:23
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And here's the question itself


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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 18:38
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pilotmike327 wrote:
I see that part is correct on my end as well but I am referencing the equation right before the paragraph that states: Solve for the store's revenue in December by multiplying both sides of this equation by 4.

The full average explanation shows:
average =2/5d + 2/10d divided by 2 = 4/10d + 1/10d divided by 2 = 5/10d divided by 2 = 1/2d times 1/2 =1/4d.
i am just curious why the equation starts with 2/5d +2/10d divided by 2 and not 2/5d + 1/10d divided by 2.

Btw, just signed up for Magoosh yesterday. Loving it so far!

Dear pilotmike327,
I'm happy to respond. :-) I'm glad that you signed up for Magoosh and are enjoying it! We aim to please! :-)

My friend, you are 100% correct!! That definitely is a mistake. The funny thing is, this was correct in all the previous editions--I checked all the editions back to the 11th edition (2005)--but in the newest edition they specifically made this one change, changing it from right to wrong!

Yes, that is a mistake: that (2/10)d should be a (1/10)d, as we see in the very next step of the same equation.

I will contact GMAC and let them know about this.

Mike :-)
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Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 18:44
Fascinating. I've long suspected that official GMAT questions and answers aren't always perfect. Thanks for sharing an example that proves my suspicion!
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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 19:15
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Even the Official GMAT questions are not always right.... Nothing is perfect. We did have a member who found a mistake in her first Quan question on the real test. She contacted the GMAC and they have admitted that indeed there was an error in the question after a review of her test. You can imagine how getting something like that on your very first question and not being able to find the correct answer would throw you off.

Don't assume anything :-)

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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 19:27
bb wrote:
Even the Official GMAT questions are not always right.... Nothing is perfect. We did have a member who found a mistake in her first Quan question on the real test. She contacted the GMAC and they have admitted that indeed there was an error in the question after a review of her test. You can imagine how getting something like that on your very first question and not being able to find the correct answer would throw you off.

Don't assume anything :-)

Posted from my mobile device


That's odd. Not sure how I'd cope with that situation myself. I guess I know better now! :-D

Did the GMAC compensate her in any way? Perhaps a higher than calculated score?
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Re: Possible error on OG GMAT 2017 [#permalink] New post   30 Jun 2016, 22:30
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Hi pilotmike327,

Here is a link to a discussion of this question in the PS Forum:

if-a-certain-toy-store-s-revenue-in-november-was-2-5-of-its-134892.html

You'll find that there are ways to approach this question that are considerably easier than just doing algebra. As far as the typo in the explanation is concerned, those types of things happen (they're called 'errata errors') - and in an 850 page book, you're bound to find several.

GMAT assassins aren't born, they're made,
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Re: Possible error on OG GMAT 2017 [#permalink] New post   03 Jul 2016, 02:21
Hi there,

I was wondering if there was another error with question 3 on page 20 of the book. The question poses the equation that

An = ( A(n+1) + A(n-2) ) /2

I calculated the answer to this equation to be A6=36, which was not one of the options.

However, the explanation of the solution starts from the following equation:

An = ( A(n-1) + A(n-2) ) /2

Would that be me missing something?

THanks for your help.

Guillaume
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Re: Possible error on OG GMAT 2017 [#permalink] New post   05 Jul 2016, 11:59
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gdavid0326 wrote:
Hi there,

I was wondering if there was another error with question 3 on page 20 of the book. The question poses the equation that

An = ( A(n+1) + A(n-2) ) /2

I calculated the answer to this equation to be A6=36, which was not one of the options.

However, the explanation of the solution starts from the following equation:

An = ( A(n-1) + A(n-2) ) /2

Would that be me missing something?

THanks for your help.

Guillaume

Dear Guillaume,
I'm happy to respond. :-)

Yes, that is another mistake. I will let the folks at GMAC know about this, if this is not on their radar already.

Mike :-)
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kapross123
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Re: Possible error on OG GMAT 2017 [#permalink] New post   09 Jul 2016, 11:26
I have found several errors so far in the OG 2017 version. Very frustrating.

One question I have is on the Diagnostic Test, #42 in the Data Sufficiency portion. The question is: "Does the integer k have at least three different positive prime factors?
1. k/15 is an integer
2. k/10 is an integer

The book says that the answer is C, both statements together are sufficient.

My question is - is 1 not a prime factor, thereby making each statement sufficient on it's own? So, the factors in 1. K/15 would be 1, 3, and 5; and factors in 2. k/10 would be 1, 2, and 5.

Thank you!
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Re: Possible error on OG GMAT 2017 [#permalink] New post   09 Jul 2016, 13:03
Kapross123 , 1 is not a prime number hence not a prime factor. The smallest prime number is 2.

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Re: Possible error on OG GMAT 2017 [#permalink] New post   09 Jul 2016, 14:36
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kapross123 wrote:
I have found several errors so far in the OG 2017 version. Very frustrating.

One question I have is on the Diagnostic Test, #42 in the Data Sufficiency portion. The question is: "Does the integer k have at least three different positive prime factors?
1. k/15 is an integer
2. k/10 is an integer

The book says that the answer is C, both statements together are sufficient.

My question is - is 1 not a prime factor, thereby making each statement sufficient on it's own? So, the factors in 1. K/15 would be 1, 3, and 5; and factors in 2. k/10 would be 1, 2, and 5.

Thank you!

Dear kapross123,
My friend, I will recommend reading carefully this blog article:
GMAT Math: One is NOT a Prime Number

The GMAT loves to snag people on this rule. It's very important to be clear on this. Does all this make sense?

Mike :-)
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Possible error on OG GMAT 2017 [#permalink] New post   15 Jul 2016, 10:30
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gdavid0326 wrote:
Hi there,

I was wondering if there was another error with question 3 on page 20 of the book. The question poses the equation that

An = ( A(n+1) + A(n-2) ) /2

I calculated the answer to this equation to be A6=36, which was not one of the options.

However, the explanation of the solution starts from the following equation:

An = ( A(n-1) + A(n-2) ) /2

Would that be me missing something?

THanks for your help.

Guillaume


It's a typo! The plus should be a minus. The equation provided in the answer explanations is the correct formula.

the-sequence-a1-a2-a3-an-is-such-that-an-an-134498.html

Someone should probably start working on an errata list for the 2017 OGs, seeing that these are 2 errors we've now discussed on this thread (1 typo in a question and 1 typo in the answer explanations), and 3 others in the answer explanations on page 121, making 5 total that I know of so far.

Yes, even the GMAC makes mistakes. Strangely comforting...
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Possible error on OG GMAT 2017 [#permalink]
15 Jul 2016, 10:30

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