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 3 of 9.
Abhinn said:
1 decade ago
Please explain what does 90 min less means?
Sireesha said:
1 decade ago
The time difference between downstream and upstream is 90 min.
Bala said:
1 decade ago
Answer: Option A.
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.
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.
Honey said:
1 decade ago
x2+48x-100 = 0.
x2+50x+2x-100 = 0.
x(x+50)-2(x+50) = 0.
(x+50)(x-2) = 0.
x = 2.
x2+50x+2x-100 = 0.
x(x+50)-2(x+50) = 0.
(x+50)(x-2) = 0.
x = 2.
Hussain peera said:
1 decade ago
Can we find solution to this problem in different manner it means any shortcut.
Ravi Kumar said:
1 decade ago
After getting X+50 and X-2 as factors of the quadratic equation, why two has been considered as answer and why not 50?
Considering X=2 is not clear. Please explain.
Considering X=2 is not clear. Please explain.
Rishabh said:
1 decade ago
How does it become (36)/(10-x)-(36)/(10+x)?
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.
Suchita said:
1 decade ago
I don't understand this, please help.
Ram said:
1 decade ago
Hello am not following how to take '+' n '-'in b/w: 36/(10-x) '-' 36/(10+x) = 90/60.
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