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 8 of 9.
Deepankar De said:
10 years ago
@Rohit.
Distance/Speed = Time.
Taking x as speed of the stream.
Upstream distance/(Still_water_speed - x) or Upstream time minus Downstream_distance/(Still_water_speed - x) or Downstream time.
Equals to 90 mins/60 dividing by 60 as we want to bring all the time values to the same unit.
This thing is already mentioned in the problem.
"A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream".
Distance/Speed = Time.
Taking x as speed of the stream.
Upstream distance/(Still_water_speed - x) or Upstream time minus Downstream_distance/(Still_water_speed - x) or Downstream time.
Equals to 90 mins/60 dividing by 60 as we want to bring all the time values to the same unit.
This thing is already mentioned in the problem.
"A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream".
Aisha gupta said:
10 years ago
Mph means what? "Miles per hr or meter per hr".
Rohit said:
10 years ago
Can anyone please explain me that how did you get 36/(10-x)-36/(10+x)?
Arun said:
10 years ago
How this equation came 36/(10-x)-36/(10+x) = 90/60?
Madhavan said:
10 years ago
Is there any other method to solve this?
Prabhat said:
9 years ago
Well done @Sowmya.
Anishghoshroy said:
1 decade ago
x2+48x-100.
= x2+50x-2x-100.
= x(x+50)-2(x+50).
= (x-2)(x+50).
= x2+50x-2x-100.
= x(x+50)-2(x+50).
= (x-2)(x+50).
Ram said:
1 decade ago
Hello am not following how to take '+' n '-'in b/w: 36/(10-x) '-' 36/(10+x) = 90/60.
Suchita said:
1 decade ago
I don't understand this, please help.
Meghana said:
1 decade ago
50 can't be the answer. Because when you solve x+50=0, Then x becomes negative. Speed cannot be negative.
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