Events & Promotions
|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
12 Sep 2017, 12:42
Kudos
Bookmarks
E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
35%
(medium)
Question Stats:
72% (01:59) correct
28%
(02:03)
wrong
based on 133
sessions
History
Date
Time
Result
Not Attempted Yet
It takes Sarah as long to paddle 10 miles downstream on a river flowing at 3 mph as it does to paddle 12 miles down a river flowing at 4 mph. How fast does Sarah paddle in still water?
A) 4 mph
B) 3 1/2 mph
C) 3 mph
D) 2 1/2 mph
E) 2 mph
Source: 800Score
A) 4 mph
B) 3 1/2 mph
C) 3 mph
D) 2 1/2 mph
E) 2 mph
Source: 800Score
12 Sep 2017, 14:47
Kudos
Bookmarks
HKD1710
It takes Sarah the same amount of time to paddle 10 miles down a river with a current of 3 mph as it does to paddle 12 miles down a river with a current of 4 mph.
Because travel times are equal, use D/r = t to find variable expressions for \(t_1\) and \(t_2\), then set \(t_1\) equal to \(t_2\) to solve for rate of Sarah's paddling.
Let x = Sarah's paddling rate in still water
First river
Distance = 10 miles
Rate = x + 3 (mph)
(Per prompt, the river current here adds 3 miles per hour to Sarah's paddling)
Time = Distance/Rate
First river TIME, \(t_1\) : \(\frac{10}{(x + 3)}\)
Second river
Distance = 12 miles
Rate = x + 4
Second river TIME, \(t_2\) : \(\frac{12}{(x + 4)}\)
Times are equal, so
\(\frac{10}{(x + 3)}\) = \(\frac{12}{(x + 4)}\)
10x + 40 = 12x + 36
4 = 2x
x = 2 mph
Answer
15 Sep 2017, 10:17
Kudos
Bookmarks
HKD1710
We can let Sarah’s rate of paddling in still water = r. When the river is flowing at 3 mph downstream, her rate is r + 3, and when the river is flowing at 4 mph downstream, her rate is r + 4.
Recall that distance = rate x time, and thus time = distance/rate. Since it It takes Sarah as long to paddle 10 miles downstream on a river flowing at 3 mph as it does to paddle 12 miles down a river flowing at 4 mph, we set the two times equal to each other:
10/(r + 3) = 12/(r + 4)
10(r + 4) = 12(r + 3)
10r + 40 = 12r + 36
4 = 2r
2 = r
Answer: E
