## Is this a misprint by GMAC

##### This topic has expert replies
Legendary Member
Posts: 1325
Joined: 01 Nov 2009
Thanked: 105 times
Followed by:14 members

### Is this a misprint by GMAC

by vikram4689 » Fri May 11, 2012 5:07 am
https://www.mba.com/the-gmat/nex-gen/sam ... 1?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
Premise: If you like my post
Conclusion : Press the Thanks Button

### GMAT/MBA Expert

GMAT Instructor
Posts: 15374
Joined: 08 Dec 2008
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1266 members
GMAT Score:770
by [email protected] » Fri May 11, 2012 7:14 am
vikram4689 wrote:https://www.mba.com/the-gmat/nex-gen/sam ... 1?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: https://www.gmatprepnow.com/module/gmat- ... ics?id=805

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com

Check out these free resources

GMAT Instructor
Posts: 1248
Joined: 29 Mar 2012
Location: Everywhere
Thanked: 503 times
Followed by:191 members
GMAT Score:780
by [email protected] » 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
Join Veritas Prep's 2010 Instructor of the Year, Matt Douglas for GMATT Mondays

Visit the Veritas Prep Blog

Try the FREE Veritas Prep Practice Test

Legendary Member
Posts: 1325
Joined: 01 Nov 2009
Thanked: 105 times
Followed by:14 members
by vikram4689 » Fri May 11, 2012 8:14 am
[email protected] wrote:
vikram4689 wrote:https://www.mba.com/the-gmat/nex-gen/sam ... 1?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: https://www.gmatprepnow.com/module/gmat- ... ics?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
Premise: If you like my post
Conclusion : Press the Thanks Button

### GMAT/MBA Expert

GMAT Instructor
Posts: 15374
Joined: 08 Dec 2008
Location: Vancouver, BC
Thanked: 5254 times
Followed by:1266 members
GMAT Score:770
by [email protected] » 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

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com

Check out these free resources

Legendary Member
Posts: 1325
Joined: 01 Nov 2009
Thanked: 105 times
Followed by:14 members
by vikram4689 » Fri May 11, 2012 8:33 am
[email protected] wrote: Having said that, if the official questions are as difficult as the ones floating around, then we're all in the same boat
Yes, they are tricky. I have gone through all 50 IR in OG13 and it seems difficult to solve 12Q in 30 min.
Premise: If you like my post
Conclusion : Press the Thanks Button

Newbie | Next Rank: 10 Posts
Posts: 4
Joined: 07 Sep 2013
by getdonewithgmat » Tue Sep 24, 2013 10:51 am
[email protected] wrote:
vikram4689 wrote:https://www.mba.com/the-gmat/nex-gen/sam ... 1?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: https://www.gmatprepnow.com/module/gmat- ... ics?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!

• Page 1 of 1
{"extraction_info": {"found_math": false, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0, "math_score": 0.87321937084198, "perplexity": 1256.0021012685966}, "config": {"markdown_headings": true, "markdown_code": true, "boilerplate_config": {"ratio_threshold": 0.18, "absolute_threshold": 10, "end_threshold": 15, "enable": true}, "remove_buttons": true, "remove_image_figures": true, "remove_link_clusters": true, "table_config": {"min_rows": 2, "min_cols": 3, "format": "plain"}, "remove_chinese": true, "remove_edit_buttons": true, "extract_latex": true}, "warc_path": "s3://commoncrawl/crawl-data/CC-MAIN-2021-10/segments/1614178378043.81/warc/CC-MAIN-20210307170119-20210307200119-00258.warc.gz"}