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.
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)
Sag said:
1 decade ago
How to solve the equation.
Actually I forget to solve these equations.
How they got x2 + 48x - 100 = (x+50)(x-2).
Actually I forget to solve these equations.
How they got x2 + 48x - 100 = (x+50)(x-2).
Suji said:
1 decade ago
we can also take like that....
it is easy to form eqn like above
ie difference between upstream and downsttream
..
it is easy to form eqn like above
ie difference between upstream and downsttream
..
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.
Noah said:
1 decade ago
Can any body explain this?
A boat takes 90 minutes "less" to travel. Then why do we write the equation = 90?
A boat takes 90 minutes "less" to travel. Then why do we write the equation = 90?
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)
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.
Venkat said:
10 years ago
Shortcut:
Distance D = 36.
Time T = 90 minutes.
90 minutes = 1.30 hrs.
D = S/T.
36 = S/1.3.
S = 2.
Distance D = 36.
Time T = 90 minutes.
90 minutes = 1.30 hrs.
D = S/T.
36 = S/1.3.
S = 2.
Sharmila G said:
5 years ago
@Sriteja.
There is "less" is given in the qn that's why we subtracting the upstream and downstream.
There is "less" is given in the qn that's why we subtracting the upstream and downstream.
(3)
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.
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