Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 8)
8.
A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:
Answer: Option
Explanation:
Let the speed of the stream x mph. Then,
Speed downstream = (10 + x) mph,
Speed upstream = (10 - x) mph.
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36 | - | 36 | = | 90 |
(10 - x) | (10 + x) | 60 |
72x x 60 = 90 (100 - x2)
x2 + 48x - 100 = 0
(x+ 50)(x - 2) = 0
x = 2 mph.
Discussion:
85 comments Page 2 of 9.
Annil Gani said:
5 years ago
Upstream ditsnace = downstream distance.
90/60*(10-x) = (10+s),
300 = 150*x,
X = 2.
90/60*(10-x) = (10+s),
300 = 150*x,
X = 2.
(10)
Guru said:
5 years ago
I am not getting this, please explain me.
(3)
Prem said:
5 years ago
Let upstream time be T hrs.
Then, downstream time will be T-3/2 hrs.
Upstream - downstream = T - T + 3/2 = 3/2 hrs = 90 minutes.
Then, downstream time will be T-3/2 hrs.
Upstream - downstream = T - T + 3/2 = 3/2 hrs = 90 minutes.
(1)
Budhiram Hembram said:
5 years ago
Let the speed of the stream be x mph.
Then sp. Downstream=(10+x) mph.
Sp. Upstream =(10-x) mph.
(36/10-x) - (36/10-x) =90/60.
Can be written as (36/10-x)- (36/10-x) = 9/6,
[360+36x-360+36x]6 = 9(10^2-x^2),
72x * 6= 900-9x^2,
9x^2+432x-900=0,
x^2 +48x -100=0.
(x+50)(x-2),
X=2mph.
Then sp. Downstream=(10+x) mph.
Sp. Upstream =(10-x) mph.
(36/10-x) - (36/10-x) =90/60.
Can be written as (36/10-x)- (36/10-x) = 9/6,
[360+36x-360+36x]6 = 9(10^2-x^2),
72x * 6= 900-9x^2,
9x^2+432x-900=0,
x^2 +48x -100=0.
(x+50)(x-2),
X=2mph.
(1)
Guna de villiers said:
6 years ago
D/S = T.
Time difference is 90.
We have to convert miles per HOUR.
So (36/10-x)-(36/10+x) = 90/60.
Time difference is 90.
We have to convert miles per HOUR.
So (36/10-x)-(36/10+x) = 90/60.
Yuvdeep Kaur said:
6 years ago
Hi, I am unable to understand this step that is 72X x 60 =90(100 - X^2).
X^2 +48X - 100 = 0.
(X +50) (X - 2).
X=2mph.
X^2 +48X - 100 = 0.
(X +50) (X - 2).
X=2mph.
(1)
Munshi Mirajul said:
6 years ago
Let stream is considered as "S"
Speed Downstream = (10+S).
Speed Upstream =(10-S).
Upstream Speed - Downstream Speed = 90/60 (minutes converted to hour).
36/(10-S) - 36(10+S) = 90/60.
36(10+S) - 36(10-S) / (10+S) (10-S) = 3/2 ( Divided those) {(10+S) and (10-S) as LCM}.
360+36S-360+36S / 100-10S+10S-S^2= 3/2 (360 and 10s Subtracted).
72S / (100-S^2) = 3/2.
144S = 300 - 3S^2 (cross Multiplication).
3S^2 + 144S - 300 = 0.
S^2 + 48S - 100 = 0 (ALL are divided by 3).
S^2 + 50S - 2S -100 =0.
S( S+50) - 2(S+50) = 0.
(S+50) (S-2) = 0.
S = - 50 (Is not granted).
S = 2.
So the speed of the stream is 2.
Speed Downstream = (10+S).
Speed Upstream =(10-S).
Upstream Speed - Downstream Speed = 90/60 (minutes converted to hour).
36/(10-S) - 36(10+S) = 90/60.
36(10+S) - 36(10-S) / (10+S) (10-S) = 3/2 ( Divided those) {(10+S) and (10-S) as LCM}.
360+36S-360+36S / 100-10S+10S-S^2= 3/2 (360 and 10s Subtracted).
72S / (100-S^2) = 3/2.
144S = 300 - 3S^2 (cross Multiplication).
3S^2 + 144S - 300 = 0.
S^2 + 48S - 100 = 0 (ALL are divided by 3).
S^2 + 50S - 2S -100 =0.
S( S+50) - 2(S+50) = 0.
(S+50) (S-2) = 0.
S = - 50 (Is not granted).
S = 2.
So the speed of the stream is 2.
(1)
Kartik said:
6 years ago
In question time taken is 90 min less. How you can add or substrate time data with speed? Please tell me.
(1)
Akash said:
6 years ago
@Siddesh.
Boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream.
It means while going downstream the time will be less and will while going upstream (i.e against) it will take 90 min more;
so t=d/s.
Boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream.
It means while going downstream the time will be less and will while going upstream (i.e against) it will take 90 min more;
so t=d/s.
Siddesh said:
6 years ago
Can anyone say please, how can we equate both the upstream and downstream to 90, if downstream takes less than 90 minutes? Please tell me.
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