Hi,
I have a doubt in the below question(from the GMAT Bible):
By what percent did the infant mortality rate in Country X
decrease from 1972 to 1976?
(1) On average, the infant mortality rate in Country X
decreased by 10% per year from 1972 to 1976.
(2) On average, the infant mortality rate in Country X
decreased by 8% per year from 1970 to 1980.
The answer provided is A. The reasoning is if m is mortality rate in 1972, then for each year it will be 0.9*(previous year's rate).
so for 1976, it will be 0.9*0.9*0.9*0.9*m.
This is fine but here the value of m is not provided.
So shouldn't the answer be E?
Rate of decrease
This topic has expert replies
GMAT/MBA Expert
- Anurag@Gurome
- GMAT Instructor
- Posts: 3835
- Joined: Fri Apr 02, 2010 10:00 pm
- Location: Milpitas, CA
- Thanked: 1854 times
- Followed by:523 members
- GMAT Score:770
Statement 1: Say, mortality rate in 1972 is msri_r wrote:By what percent did the infant mortality rate in Country X decrease from 1972 to 1976?
(1) On average, the infant mortality rate in Country X decreased by 10% per year from 1972 to 1976.
(2) On average, the infant mortality rate in Country X decreased by 8% per year from 1970 to 1980.
Hence, mortality rate in 1976 is (0.9^4)*m
Hence, percentage decrease = [(m - (0.9^4)*m)/m]*100 = [1 - (0.9^4)]*100 ---> A definite value
Sufficient
Statement 2: This is not enough to determine the required percentage as we do not know what happened to the mortality rate in the particular period 1972 to 1976
Not sufficient
The correct answer is A.
We do not need the value of m as the question did not asked for the mortality rate in 1976.sri_r wrote:...This is fine but here the value of m is not provided.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
-
- Master | Next Rank: 500 Posts
- Posts: 298
- Joined: Tue Feb 16, 2010 1:09 am
- Thanked: 2 times
- Followed by:1 members
Can we not assume the mortality rate for the year of 1970 as m, hence for 1972 it would be 0.92*0.92m and for 1976 0.92^6 m . So that wouldn't that be sufficient to calculate the percent decrease.
- GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
This is a DS problem.sri_r wrote:By what percent did the infant mortality rate in Country X decrease from 1972 to 1976?
(1) On average, the infant mortality rate in Country X decreased by 10% per year from 1972 to 1976.
(2) On average, the infant mortality rate in Country X decreased by 8% per year from 1970 to 1980.
Do only as much calculating as necessary.
Statement 1: On average, the infant mortality rate in Country X decreased by 10% per year from 1972 to 1976.
Since we know the average percent decrease each year, we can calculate the total percent decrease for the entire period.
SUFFICIENT.
Statement 2: On average, the infant mortality rate in Country X decreased by 8% per year from 1970 to 1980.
Here, the SUM of the percent decreases for the entire 10 years = number*average = 10*8 = 80.
It's possible that the average percent decrease each year from 1972 to 1976 was 20%, while the average percent decrease for the remaining 6 years was 0%, since (4*20) + (6*0) = 80.
It's possible that the average percent decrease each of the 10 years -- including from 1972 to 1976 -- was 8%.
Since different percent decreases are possible, INSUFFICIENT.
The correct answer is A.
Last edited by GMATGuruNY on Thu Aug 08, 2013 6:11 am, edited 1 time in total.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Deepthi Subbu wrote:Can we not assume the mortality rate for the year of 1970 as m, hence for 1972 it would be 0.92*0.92m and for 1976 0.92^6 m . So that wouldn't that be sufficient to calculate the percent decrease.
For both statements, we are not told the individual percent decreases from year to year.
For statement 1, the individual percent decreases from year to year don't matter, because we're told that the average yearly decreases from 1972 to 1976, the exact same timeframe as in the target question.
In statement 2, because we're told that the average yearly decreases from 1970 to 1980. So, it could be the case that, between 1972 and 1976, there was a 1% decrease each year, then there were considerably bigger decreases during the other years (to create an overall average decrease of 8% for the 10 years). Or, it could be the case that, between 1972 and 1976, there was a 8% decrease each year. There's no way to be certain.
I hope that helps.
Cheers,
Brent