Last year Harold's average time to finish the qualifying event was three hours. If he knows that he can increase his speed this year by 20%, how many minutes should it take him to complete the event?
A-150
B-144
C-120
D-90
E-36
I know this is very simple prob.I am getting ans B but OA is A
Help
Harold's Time
This topic has expert replies
-
- Master | Next Rank: 500 Posts
- Posts: 126
- Joined: Sat Jun 07, 2014 5:26 am
- Thanked: 3 times
-
- Master | Next Rank: 500 Posts
- Posts: 363
- Joined: Sun Oct 17, 2010 3:24 pm
- Thanked: 115 times
- Followed by:3 members
The distance before and after will be the same.sandipgumtya wrote:Last year Harold's average time to finish the qualifying event was three hours. If he knows that he can increase his speed this year by 20%, how many minutes should it take him to complete the event?
A-150
B-144
C-120
D-90
E-36
I know this is very simple prob.I am getting ans B but OA is A
Help
speed = distance/time
distance = speed x time
therefore speed before x time before = new speed x new time
S X T = 1.2S X T/1.2
T/1.2 = 180/1.2 = 1800/12 = 150
ANS= A
- 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
20% faster = 120% of last year's speed = 6/5 of last year's speed.sandipgumtya wrote:Last year Harold's average time to finish the qualifying event was three hours. If he knows that he can increase his speed this year by 20%, how many minutes should it take him to complete the event?
A-150
B-144
C-120
D-90
E-36
Rate and time are RECIPROCALS.
6/5 of last year's speed implies 5/6 of last year's time:
(5/6)(3 hours) = (5/6)(180 minutes) = 150 minutes.
The correct answer is A.
Alternate approach:
Let last year's speed = 10 feet per minute.
Since last year Harold traveled at a speed of 10 feet per minute for 180 minutes, the total distance = rt = 10*180 = 1800 feet.
If the speed is increased by 20% to 12 feet per minute, the time to travel 1800 feet = d/r = 1800/12 = 150 minutes.
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..
My approach,
1. rate x time = distance
2. Convert 3 hours to 180 mins as all answer options are minutes
3. LY - r x 180 = d
4. TY - (120/100)r x t = d
5. Solve #4 after substituting value of d from #3
6. (12/10)t = 180 --> t = 150
Bullzi
My approach,
1. rate x time = distance
2. Convert 3 hours to 180 mins as all answer options are minutes
3. LY - r x 180 = d
4. TY - (120/100)r x t = d
5. Solve #4 after substituting value of d from #3
6. (12/10)t = 180 --> t = 150
Bullzi
-
- Master | Next Rank: 500 Posts
- Posts: 126
- Joined: Sat Jun 07, 2014 5:26 am
- Thanked: 3 times
GMAT/MBA Expert
- [email protected]
- Elite Legendary Member
- Posts: 10392
- Joined: Sun Jun 23, 2013 6:38 pm
- Location: Palo Alto, CA
- Thanked: 2867 times
- Followed by:511 members
- GMAT Score:800
Hi sandipgumtya,
We're told that the SPEED is 20% faster; with your math, you're attempting to manipulate the TIME, which is why that result is incorrect.
GMAT assassins aren't born, they're made,
Rich
We're told that the SPEED is 20% faster; with your math, you're attempting to manipulate the TIME, which is why that result is incorrect.
GMAT assassins aren't born, they're made,
Rich
-
- Master | Next Rank: 500 Posts
- Posts: 126
- Joined: Sat Jun 07, 2014 5:26 am
- Thanked: 3 times
As speed and time are inversely proportional,20% faster means 20% lesser time.Is this concept wrong. Pl correct me in detail.
GMAT/MBA Expert
- [email protected]
- Elite Legendary Member
- Posts: 10392
- Joined: Sun Jun 23, 2013 6:38 pm
- Location: Palo Alto, CA
- Thanked: 2867 times
- Followed by:511 members
- GMAT Score:800
Hi sandipgymtya,
Percent Change is calculated based on the ORIGINAL numbers involved. While speed and time ARE related, their respective percent changes are NOT the same.
Assuming that the distance stays the same, Increasing a speed by 20% decreases the time by 16 1/6% (not 20%).
Here's why:
Original speed and time:
D = (R)(T)
20% increase in speed:
D = (6/5)(R)(5/6)(T)
Since the distance is the same, the (6/5) is 'cancelled out' by the (5/6) - the speed increased by 1/5 (or 20%), but the time decreased by 1/6 (or 16 1/6%).
GMAT assassins aren't born, they're made,
Rich
Percent Change is calculated based on the ORIGINAL numbers involved. While speed and time ARE related, their respective percent changes are NOT the same.
Assuming that the distance stays the same, Increasing a speed by 20% decreases the time by 16 1/6% (not 20%).
Here's why:
Original speed and time:
D = (R)(T)
20% increase in speed:
D = (6/5)(R)(5/6)(T)
Since the distance is the same, the (6/5) is 'cancelled out' by the (5/6) - the speed increased by 1/5 (or 20%), but the time decreased by 1/6 (or 16 1/6%).
GMAT assassins aren't born, they're made,
Rich
-
- Master | Next Rank: 500 Posts
- Posts: 126
- Joined: Sat Jun 07, 2014 5:26 am
- Thanked: 3 times
- 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
As noted above:sandipgumtya wrote:As speed and time are inversely proportional,20% faster means 20% lesser time.Is this concept wrong. Pl correct me in detail.
20% faster = (120/100)r = (6/5)r.
Since rate and time are reciprocals:
(6/5)r --> (5/6)t --> 1/6 less time.
Other examples:
50% faster = (150/100)r = (3/2)r.
Since rate and time are reciprocals:
(3/2)r --> (2/3)t --> 1/3 less time.
20% slower = (80/100)r = (4/5)r.
Since rate and time are reciprocals:
(4/5)r --> (5/4)t = 1/4 more time.
50% slower = (50/100)r = (1/2)r.
Since rate and time are reciprocals:
(1/2)r --> 2t --> twice the time.
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
- Jeff@TargetTestPrep
- GMAT Instructor
- Posts: 1462
- Joined: Thu Apr 09, 2015 9:34 am
- Location: New York, NY
- Thanked: 39 times
- Followed by:22 members
Recall that rate x time = job (or rate = job/time, or time = job/rate). Since Harold's time to complete the event was 3 hours, we can say that his rate was 1 job per 3 hours; i.e., his rate is 1/3. Since he's increasing his speed by 20%, his new rate is:sandipgumtya wrote:Last year Harold's average time to finish the qualifying event was three hours. If he knows that he can increase his speed this year by 20%, how many minutes should it take him to complete the event?
A-150
B-144
C-120
D-90
E-36
(1/3) x 1.2
(1/3) x 12/10 = 4/10 = 2/5
Since his new rate is 2/5, his new time is 1/(2/5) = 5/2 = 2.5 hours. Thus he can complete the event in 2.5 x 60 = 150 minutes.
Answer: A
Jeffrey Miller
Head of GMAT Instruction
[email protected]
See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews