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 6 of 9.
Gopal said:
1 decade ago
Downstream-upstream = ((36/(10+x)) - ((36/(10-x)) ;
I have tried with this I got clarification if any one has any doubt check with this.
Thank you.
I have tried with this I got clarification if any one has any doubt check with this.
Thank you.
Kavitha said:
1 decade ago
(x+ 50)(x - 2) = 0 how this step come from x2 + 48x + 100 = 0.
This equations please explain?
This equations please explain?
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).
Chandhu said:
1 decade ago
Speed=distance/time.
They had given that, the time difference between upstream and downstream as 90 min or 90/60 hours.
We know the relation that: speed=distance/time.
From that time=distance/speed.
Therefore: upstream time-downstream time= (upstream distance/upstream speed) - (downstream distance/downstream speed).
Which is equal to:.
90/60 hours= (36/10-X) - (36/10+X). (X=speed of stream).
From this by solving the equation we can get the X value as 2 miles/hour).
Therefore speed of stream=2 miles/hour (mph).
They had given that, the time difference between upstream and downstream as 90 min or 90/60 hours.
We know the relation that: speed=distance/time.
From that time=distance/speed.
Therefore: upstream time-downstream time= (upstream distance/upstream speed) - (downstream distance/downstream speed).
Which is equal to:.
90/60 hours= (36/10-X) - (36/10+X). (X=speed of stream).
From this by solving the equation we can get the X value as 2 miles/hour).
Therefore speed of stream=2 miles/hour (mph).
Sireesha said:
1 decade ago
The time difference between downstream and upstream is 90 min.
Rohit Chavan said:
1 decade ago
Downstream speed = (upstream speed-90); _____(because downstream takes 90 min less then upstream.)
Hence, (90/60)min=(36/(10-x))+(36/(10+x));
and proceed as given in solution i.e. simplify the equation.
Hence, (90/60)min=(36/(10-x))+(36/(10+x));
and proceed as given in solution i.e. simplify the equation.
Rohit chavan said:
1 decade ago
Given Condition:(upstream speed-(90/60)min)=downstream speed;
we know,
time=distance/speed;
(90/60)min=(upstream distance/upstream speed)+
(downstream distance/downstream speed)
(90/60)min=(36/(10-x))+(36/(10+x));
we know,
time=distance/speed;
(90/60)min=(upstream distance/upstream speed)+
(downstream distance/downstream speed)
(90/60)min=(36/(10-x))+(36/(10+x));
Keerthan said:
1 decade ago
I didn't get from wer did the 60/90 ratio come! can anybody?
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
..
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?
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