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Is this a misprint by GMAC

This topic has 3 expert replies and 3 member replies
vikram4689 Legendary Member
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Is this a misprint by GMAC

Post Fri May 11, 2012 5:07 am
http://www.mba.com/the-gmat/nex-gen/samples/Sample-701?next=yes

Checkout the Q1 in above link. Given answer is 4000-5000yrs. For this to be true sum of ages should be at least 4000*3=12000yrs

Calculating the sum = 900+3000+5300=9200yrs (which is < 12000yrs)

I can't find anything wrong here but i also know that GMAC is never wrong

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Post Fri May 11, 2012 7:14 am
vikram4689 wrote:
http://www.mba.com/the-gmat/nex-gen/samples/Sample-701?next=yes

Checkout the Q1 in above link. Given answer is 4000-5000yrs. For this to be true sum of ages should be at least 4000*3=12000yrs

Calculating the sum = 900+3000+5300=9200yrs (which is < 12000yrs)

I can't find anything wrong here but i also know that GMAC is never wrong
The question asks us to consider "all integer values of the age from 12 to 30."
In your solution, you are considering the ages 12, 16 and 20 only.

We actually need to find the mass at ages 12, 13, 14, . . . 29, and 30, and then find the average of these masses.

Now, of course the GMAC doesn't want to perform such a tedious calculation. Instead, we need to get a feel for the average.

First notice that from ages 12 to 20, the increases are somewhat constant. In other words, since that curve from points A to C is close to straight, it looks like the T-Rex's mass increases by the approximately the same amount each year. There's a nice rule that deals with the average of a set of values when those values are equally spaced: In a set where the numbers are equally spaced, the mean will equal the median.

So, if we examine only the masses from ages 12 to 20, the average mass will be approximately equal to the median mass. This median mass will occur in the middle, at age 16.

The T-Rex's mass at at 16 is about 3000 kg, so we can conclude that, during the 8 years between ages 12 to 20, the T-Rex's average mass is 3000 kg.

Now notice that, from ages 21 to 30, T-Rex's average mass is about 5500 kg.

At this point, we have a weighted averages question.

Ages 12 to 20: During these 8 years the average mass is about 3000 kg
Ages 21 to 30: During these 10 years the average mass is about 5500 kg

Given this, we can see that the average mass during the entire 18-year period will be closer to 5500 than it is to 3000.

So, the average mass must be greater than 4250 kg (which is halfway between 3000 and 5500).

I cover this concept of weighted averages in the following video: http://www.gmatprepnow.com/module/gmat-statistics?id=805

Cheers,
Brent

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Bill@VeritasPrep GMAT Instructor
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Post Fri May 11, 2012 7:33 am
vikram4689 wrote:
I can't find anything wrong here but i also know that GMAC is never wrong
My copy of OG12 would disagree Wink

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vikram4689 Legendary Member
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Post Fri May 11, 2012 8:14 am
Brent@GMATPrepNow wrote:
vikram4689 wrote:
http://www.mba.com/the-gmat/nex-gen/samples/Sample-701?next=yes

Checkout the Q1 in above link. Given answer is 4000-5000yrs. For this to be true sum of ages should be at least 4000*3=12000yrs

Calculating the sum = 900+3000+5300=9200yrs (which is < 12000yrs)

I can't find anything wrong here but i also know that GMAC is never wrong
The question asks us to consider "all integer values of the age from 12 to 30."
In your solution, you are considering the ages 12, 16 and 20 only.

We actually need to find the mass at ages 12, 13, 14, . . . 29, and 30, and then find the average of these masses.

Now, of course the GMAC doesn't want to perform such a tedious calculation. Instead, we need to get a feel for the average.

First notice that from ages 12 to 20, the increases are somewhat constant. In other words, since that curve from points A to C is close to straight, it looks like the T-Rex's mass increases by the approximately the same amount each year. There's a nice rule that deals with the average of a set of values when those values are equally spaced: In a set where the numbers are equally spaced, the mean will equal the median.

So, if we examine only the masses from ages 12 to 20, the average mass will be approximately equal to the median mass. This median mass will occur in the middle, at age 16.

The T-Rex's mass at at 16 is about 3000 kg, so we can conclude that, during the 8 years between ages 12 to 20, the T-Rex's average mass is 3000 kg.

Now notice that, from ages 21 to 30, T-Rex's average mass is about 5500 kg.

At this point, we have a weighted averages question.

Ages 12 to 20: During these 8 years the average mass is about 3000 kg
Ages 21 to 30: During these 10 years the average mass is about 5500 kg

Given this, we can see that the average mass during the entire 18-year period will be closer to 5500 than it is to 3000.

So, the average mass must be greater than 4250 kg (which is halfway between 3000 and 5500).

I cover this concept of weighted averages in the following video: http://www.gmatprepnow.com/module/gmat-statistics?id=805

Cheers,
Brent
Thanks Brent, i find IR ques. convoluted and 2:30 min is less to understand that convoluted language and then answer 2-3 True/False type assertions. Can you suggest some way how i should proceed.

I find Graphs, Charts etc. easy to comprehend but somehow i am not able to answer all parts of a question correctly and that means 0 credit for that question. Most of my error are because of convoluted language of question

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Post Fri May 11, 2012 8:20 am
vikram4689 wrote:
Thanks Brent, i find IR ques. convoluted and 2:30 min is less to understand that convoluted language and then answer 2-3 True/False type assertions. Can you suggest some way how i should proceed.

I find Graphs, Charts etc. easy to comprehend but somehow i am not able to answer all parts of a question correctly and that means 0 credit for that question. Most of my error are because of convoluted language of question
I concur. The GMAC's exemplar questions are quite tricky, and hard to complete in 2.5 minutes. I have a feeling that the actual IR questions you see on test day will be easier than the ones floating around.

Having said that, if the official questions are as difficult as the ones floating around, then we're all in the same boat Smile

Cheers,
Brent

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vikram4689 Legendary Member
Joined
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Post Fri May 11, 2012 8:33 am
Brent@GMATPrepNow wrote:
Having said that, if the official questions are as difficult as the ones floating around, then we're all in the same boat Smile
Yes, they are tricky. I have gone through all 50 IR in OG13 and it seems difficult to solve 12Q in 30 min.

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getdonewithgmat Newbie | Next Rank: 10 Posts Default Avatar
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Post Tue Sep 24, 2013 10:51 am
Brent@GMATPrepNow wrote:
vikram4689 wrote:
http://www.mba.com/the-gmat/nex-gen/samples/Sample-701?next=yes

Checkout the Q1 in above link. Given answer is 4000-5000yrs. For this to be true sum of ages should be at least 4000*3=12000yrs

Calculating the sum = 900+3000+5300=9200yrs (which is < 12000yrs)

I can't find anything wrong here but i also know that GMAC is never wrong
The question asks us to consider "all integer values of the age from 12 to 30."
In your solution, you are considering the ages 12, 16 and 20 only.

We actually need to find the mass at ages 12, 13, 14, . . . 29, and 30, and then find the average of these masses.

Now, of course the GMAC doesn't want to perform such a tedious calculation. Instead, we need to get a feel for the average.

First notice that from ages 12 to 20, the increases are somewhat constant. In other words, since that curve from points A to C is close to straight, it looks like the T-Rex's mass increases by the approximately the same amount each year. There's a nice rule that deals with the average of a set of values when those values are equally spaced: In a set where the numbers are equally spaced, the mean will equal the median.

So, if we examine only the masses from ages 12 to 20, the average mass will be approximately equal to the median mass. This median mass will occur in the middle, at age 16.

The T-Rex's mass at at 16 is about 3000 kg, so we can conclude that, during the 8 years between ages 12 to 20, the T-Rex's average mass is 3000 kg.

Now notice that, from ages 21 to 30, T-Rex's average mass is about 5500 kg.

At this point, we have a weighted averages question.

Ages 12 to 20: During these 8 years the average mass is about 3000 kg
Ages 21 to 30: During these 10 years the average mass is about 5500 kg

Given this, we can see that the average mass during the entire 18-year period will be closer to 5500 than it is to 3000.

So, the average mass must be greater than 4250 kg (which is halfway between 3000 and 5500).

I cover this concept of weighted averages in the following video: http://www.gmatprepnow.com/module/gmat-statistics?id=805

Cheers,
Brent
Hi Brent, i took the total number of years as 19, 12 to 20 (including 12 and 20) - 9 years and 21 to 30 (incl 21 and 30) - 10 years. Please can you confirm that this is correct or is it 18 years and if i have confused the way we count the number of years?

Thanks!

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