GMATPrep Question Pack 1
This topic has expert replies
- eagleeye
- Legendary Member
- Posts: 520
- Joined: Sat Apr 28, 2012 9:12 pm
- Thanked: 339 times
- Followed by:49 members
- GMAT Score:770
Hi Massi:
The OA should be D.
We are given speed from a-b = Sab = 80; speed from b-c = Sbc =60
1) Average speed = (total distance)/(total time);
let distance from b-c = d; then distance from a-b = 4d;
then time from b-c = distance/speed = d/60 ; time from a-b = 4d/80.
Then average speed = (d+4d)/(d/60+4d/80) = 5/(1/60+4/80) , Therefore sufficient.
2) In the same way, now let time from b-c = t ; then time from a-b = 3t
then distance from b-c = time*speed = 80t ; a-b = 60t.
then average speed = (80t+60t)/(3t+t) = 140/4 ; SUFFICIENT
Hence D
Let me know if this helps
The OA should be D.
We are given speed from a-b = Sab = 80; speed from b-c = Sbc =60
1) Average speed = (total distance)/(total time);
let distance from b-c = d; then distance from a-b = 4d;
then time from b-c = distance/speed = d/60 ; time from a-b = 4d/80.
Then average speed = (d+4d)/(d/60+4d/80) = 5/(1/60+4/80) , Therefore sufficient.
2) In the same way, now let time from b-c = t ; then time from a-b = 3t
then distance from b-c = time*speed = 80t ; a-b = 60t.
then average speed = (80t+60t)/(3t+t) = 140/4 ; SUFFICIENT
Hence D
Let me know if this helps
- 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
Statement 2: The amount of time that it took the train to travel from Station A to Station B was 3 times that amount of time that it took the train to travel from Station B to Station C.What was the average speed at which the train traveled from Station A to Station C?
Thus, of every 4 hours traveled, 3 hours are traveled at 80 miles per hour and 1 hour is traveled at 60 miles per hour, implying that the average speed every 4 hours = (3*80 + 1*60)/4 = 300/4 = 75 miles per hour.
SUFFICIENT.
Statement 1: The distance that the train traveled from Station A to Station B was 4 times the distance that the train traveled from Station B to Station C.
Learn from Statement 2:
3 hours from A to B at 80 miles per hour = 240 miles.
1 hour from B to C at 60 miles per hour = 60 miles.
When the train travels for the times given in statement 2, the distance from A to B is 4 times the distance from B to C.
Thus, the two statements tell the SAME INFORMATION.
Thus, since statement 2 is sufficient, statement 1 must also be SUFFICIENT.
The correct answer is D.
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
Hello Eagle eye,eagleeye wrote:Hi Massi:
The OA should be D.
We are given speed from a-b = Sab = 80; speed from b-c = Sbc =60
1) Average speed = (total distance)/(total time);
let distance from b-c = d; then distance from a-b = 4d;
then time from b-c = distance/speed = d/60 ; time from a-b = 4d/80.
Then average speed = (d+4d)/(d/60+4d/80) = 5/(1/60+4/80) , Therefore sufficient.
2) In the same way, now let time from b-c = t ; then time from a-b = 3t
then distance from b-c = time*speed = 80t ; a-b = 60t.
then average speed = (80t+60t)/(3t+t) = 140/4 ; SUFFICIENT
Hence D
Let me know if this helps
I lke your algebraic approach which was my first approach also, but is it correct to use the same variable for the two different distances?
I tried using 2 different variables for distance ab and bc, but maybe this was a mistake from my part.
Any thoughts?
- Bill@VeritasPrep
- GMAT Instructor
- Posts: 1248
- Joined: Thu Mar 29, 2012 2:57 pm
- Location: Everywhere
- Thanked: 503 times
- Followed by:192 members
- GMAT Score:780
Since we have a relationship between the distances, using one variable (d and 4d) works better than assigning two variables.lazarogb wrote:Hello Eagle eye,eagleeye wrote:Hi Massi:
The OA should be D.
We are given speed from a-b = Sab = 80; speed from b-c = Sbc =60
1) Average speed = (total distance)/(total time);
let distance from b-c = d; then distance from a-b = 4d;
then time from b-c = distance/speed = d/60 ; time from a-b = 4d/80.
Then average speed = (d+4d)/(d/60+4d/80) = 5/(1/60+4/80) , Therefore sufficient.
2) In the same way, now let time from b-c = t ; then time from a-b = 3t
then distance from b-c = time*speed = 80t ; a-b = 60t.
then average speed = (80t+60t)/(3t+t) = 140/4 ; SUFFICIENT
Hence D
Let me know if this helps
I lke your algebraic approach which was my first approach also, but is it correct to use the same variable for the two different distances?
I tried using 2 different variables for distance ab and bc, but maybe this was a mistake from my part.
Any thoughts?
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
Visit the Veritas Prep Blog
Try the FREE Veritas Prep Practice Test
- mcdesty
- Master | Next Rank: 500 Posts
- Posts: 116
- Joined: Wed Mar 14, 2012 1:02 pm
- Thanked: 20 times
- Followed by:11 members
- GMAT Score:760
My scratch paper looked like this when I tackled this one.
- Attachments
-
I have made your mistakes before.
I am experienced - I have tutored calculus and linear algebra for over two years.
For a very modest fee, I will ensure that your GMAT journey is a smooth one: Daily assignments and careful micro management.
PM me so we can get started.
I am experienced - I have tutored calculus and linear algebra for over two years.
For a very modest fee, I will ensure that your GMAT journey is a smooth one: Daily assignments and careful micro management.
PM me so we can get started.