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31 May 2022, 02:30
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B
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
85%
(hard)
Question Stats:
55% (03:12) correct
45%
(03:03)
wrong
based on 110
sessions
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A man travels by a motor boat down a river to his office and back. With the speed of the river unchanged, if he doubles the speed of his motor boat, then his total travel time gets reduced by 75%. The ratio of the original speed of the motor boat to the speed of the river is:
A. √6 : √2
B. √7 : 2
C. 2√5 : 3
D. 3 : 2
E. √5 : 3
Are You Up For the Challenge: 700 Level Questions
A. √6 : √2
B. √7 : 2
C. 2√5 : 3
D. 3 : 2
E. √5 : 3
Are You Up For the Challenge: 700 Level Questions
wadhwakaran
Joined: 31 Mar 2022
Last visit: 22 Jul 2025
Posts: 260
Given Kudos: 19
Location: India
Concentration: General Management, International Business
Schools: INSEAD Aug'24 intake Oxford Said'25 Judge '25 Imperial'25 HEC Sep'24 Intake LBS '26 ISB '27
GMAT 1: 700 Q50 V35
GPA: 2.8
Products:
Schools: INSEAD Aug'24 intake Oxford Said'25 Judge '25 Imperial'25 HEC Sep'24 Intake LBS '26 ISB '27
GMAT 1: 700 Q50 V35
Posts: 260
31 May 2022, 02:51
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D/B+R + D/B-R = Ti (total time taken to cover to and fro from office)
D/2B+R + D/2B-R = Tf (total time taken to cover to and fro from office)
Tf = 25% Ti = Ti/4
Solving the above 02 equations, B/R = sq. root (7)/2
D- Distance between Office & Home
B- Speed of Boat
R- Speed of River
D/B+R= Time taken to go downstream
D/B-R= Time taken to go upstream
D/2B+R= Time taken to go downstream when boat speed was doubled
D/2B-R= Time taken to go upstream when boat speed was doubled
D/2B+R + D/2B-R = Tf (total time taken to cover to and fro from office)
Tf = 25% Ti = Ti/4
Solving the above 02 equations, B/R = sq. root (7)/2
D- Distance between Office & Home
B- Speed of Boat
R- Speed of River
D/B+R= Time taken to go downstream
D/B-R= Time taken to go upstream
D/2B+R= Time taken to go downstream when boat speed was doubled
D/2B-R= Time taken to go upstream when boat speed was doubled
25 Jun 2023, 06:18
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let boat speed be B and river speed be R. We need to find B/R
While downstream, the total effective speed is B+R. while upstream, since he is moving against the tide, the total effective speed is B-R. Let distance be D and time taken usually is T.
So the first equation is T = (D/(B+R)) + (D/(B-R))
Given, that B becomes 2B , T becomes 75% LESS i.e., T/4. So our next equation is
T/4 = (D/(2B+R)) + (D/(2B-R))
Placing T from first equation in second, we get to a equation like (B/R)^2 = 7/4. thus the answer is root(7):2 => option B
While downstream, the total effective speed is B+R. while upstream, since he is moving against the tide, the total effective speed is B-R. Let distance be D and time taken usually is T.
So the first equation is T = (D/(B+R)) + (D/(B-R))
Given, that B becomes 2B , T becomes 75% LESS i.e., T/4. So our next equation is
T/4 = (D/(2B+R)) + (D/(2B-R))
Placing T from first equation in second, we get to a equation like (B/R)^2 = 7/4. thus the answer is root(7):2 => option B
