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.
 |
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 4 of 9.
Harshi said:
8 years ago
36/ (10-x) -36/ (10+x).
Why had we done subtraction here? it means why won't we did addition? Please explain.
Why had we done subtraction here? it means why won't we did addition? Please explain.
Soumajit Bose said:
8 years ago
If the boat takes 90 minutes more, then what shall we do?
Oni said:
8 years ago
36/(10-x)-36/(10+x) = 90/60,
=> 36/(10-x)-36/(10+x) = 3/2,
=> 12/(10-x)-12/(10+x) = 1/2,
=> 12(10+x)-12(10-x)/(10-x)(10+x) = 1/2,
=> 24(10+x)-24(10-x) = (10-x)(10+x),
=> 48x = 100-x^2,
=> x^2+50x-2x-100 = 0,
=> (x+50)(x-2) = 0,
=> x = 2.
=> 36/(10-x)-36/(10+x) = 3/2,
=> 12/(10-x)-12/(10+x) = 1/2,
=> 12(10+x)-12(10-x)/(10-x)(10+x) = 1/2,
=> 24(10+x)-24(10-x) = (10-x)(10+x),
=> 48x = 100-x^2,
=> x^2+50x-2x-100 = 0,
=> (x+50)(x-2) = 0,
=> x = 2.
Vijay said:
8 years ago
36(10 + x) - 36(10 - x) = 90\60.
How to solve this?
How to solve this?
(1)
Deepesh said:
9 years ago
@Chandhu.
Time taken = time taken upstream + time taken downstream.
i.e.
90/60 hrs = (18/10-x)+(18/10+x).
Then, why 90/60 hrs = (36/10-x)-(36/10+x)?
Time taken = time taken upstream + time taken downstream.
i.e.
90/60 hrs = (18/10-x)+(18/10+x).
Then, why 90/60 hrs = (36/10-x)-(36/10+x)?
Raj said:
9 years ago
D=S/T or D=S * T @ Venkat.
Raj said:
9 years ago
@Venkat.
How
36=S/1.3
S= 2.
Explain this step.
How
36=S/1.3
S= 2.
Explain this step.
Mariyada Ramesh said:
9 years ago
I too have the same doubt @Ram.
Please clear it.
Please clear it.
Kalpana said:
9 years ago
Given.
(up_stream time) - (down_stream time) = 90mins.
36(miles)/(10-x) - 36/(10+x) = 90/60.
We get equation form of
x^2 + 48x - 100 = 0.
Hence, x = 2 and x = -50.
x = 2 is the answer.
(up_stream time) - (down_stream time) = 90mins.
36(miles)/(10-x) - 36/(10+x) = 90/60.
We get equation form of
x^2 + 48x - 100 = 0.
Hence, x = 2 and x = -50.
x = 2 is the answer.
Saranya said:
9 years ago
(90/60)min = (36/(10 - x)) - (36/(10 + x));
How the minus comes between this?
How the minus comes between this?
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