Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 13)
13.
Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:
Answer: Option
Explanation:
Speed upstream = 7.5 kmph.
Speed downstream = 10.5 kmph.
 Total time taken = |
 |
105 | + | 105 |  hours = 24 hours. |
| 7.5 | 10.5 |
Discussion:
24 comments Page 1 of 3.
Prasad Nangarale said:
3 years ago
Upstream speed = 9 - 1.5 = 7.5kmph.
Downstream speed = 9+1.5 =10.5kmph.
s = d/t
t = d/s...[in both case of upstream and downstream so addition of both].
t = 105/7.5 + 105/10.5.
Multiply by 10, to remove the denominator point;
t = (105*10/75) + (105*10/105).
t= 14 + 10.
t= 24hrs.
Downstream speed = 9+1.5 =10.5kmph.
s = d/t
t = d/s...[in both case of upstream and downstream so addition of both].
t = 105/7.5 + 105/10.5.
Multiply by 10, to remove the denominator point;
t = (105*10/75) + (105*10/105).
t= 14 + 10.
t= 24hrs.
(6)
Rajat Kumar Kara said:
4 years ago
Guys, It's given the Speed of a boat in standing water and asking for the time taken by man to travel upstream and downstream. How you guys calculate upstream and downstream for the man?
Can't get it, Please explain.
Can't get it, Please explain.
Ranvijay said:
5 years ago
How it is taken 7.5 for upstream? please explain.
VIJAY . C said:
6 years ago
Upstream speed = 9 - 1.5 = 7.5kmph.
Downstream speed = 9+1.5 = 10.5kmph.
D = S * T
D = 105kmph, S in upstream = 7.5kmph.
T has taken in upstream = 105/7.5.
Similarly,
T has taken in downstream = 105/10.5.
Total time taken = ( 105/7.5.)+ (105/10.5).
Multiply by 10,
T = (105*10/75) + (105*10/105).
T = 14 + 10.
T = 24hrs.
Downstream speed = 9+1.5 = 10.5kmph.
D = S * T
D = 105kmph, S in upstream = 7.5kmph.
T has taken in upstream = 105/7.5.
Similarly,
T has taken in downstream = 105/10.5.
Total time taken = ( 105/7.5.)+ (105/10.5).
Multiply by 10,
T = (105*10/75) + (105*10/105).
T = 14 + 10.
T = 24hrs.
Aman said:
7 years ago
U.S = 1/2(P+Q).
D.S = 1/2(P-Q).
D.S = 1/2(P-Q).
Rajesh said:
7 years ago
As we know speed of the boat is U and the speed of the stream is V,
For Upstream speed=U-V (9-1.5).
For downstream speed = U+V (9+1.5).
what he mentioned is he rows against the stream with a distance of 105km.
in order to find the total time took i.e., T=D/S.
so, T=105/10.5 + 105/7.5 (downstream) = 24hrs.
For Upstream speed=U-V (9-1.5).
For downstream speed = U+V (9+1.5).
what he mentioned is he rows against the stream with a distance of 105km.
in order to find the total time took i.e., T=D/S.
so, T=105/10.5 + 105/7.5 (downstream) = 24hrs.
(1)
Dhiraj sinha said:
7 years ago
Guys look current or speed of boat mean v and in still water or stationary means u.
So for down u+v and for upstream u-v. So calculate the time by t=d/s and add both the time.
So for down u+v and for upstream u-v. So calculate the time by t=d/s and add both the time.
Priti kumari said:
7 years ago
How did we get that once it was upstream and next time it was downstream?
Divyanjali said:
8 years ago
The upstream and downstream speeds are calculated on relative motion.
If two bodies are moving in the same direction their speed is substracted and if they're moving in an opposite direction they are added.
If two bodies are moving in the same direction their speed is substracted and if they're moving in an opposite direction they are added.
Atul Kumar Singh said:
9 years ago
Guys, it's very simple you don't need to find upstream or downstream speed you can the total time like this.
Let T be total time and t1=return time and t2=going time and D = be the distance(105) x=still water speed of man and y=stream speed so,
T = t1+t2
T = (D/x+y)+(D/x-y) {definitely one direction will be upstream n oppsite dir will b downstream}
T = D{(2x)/(x^2 - y^2).
Solution.
T = (105 *2*9)/(9^2-1.5^2).
T = (1890)/(78.75),
T = 24 Hours.
Let T be total time and t1=return time and t2=going time and D = be the distance(105) x=still water speed of man and y=stream speed so,
T = t1+t2
T = (D/x+y)+(D/x-y) {definitely one direction will be upstream n oppsite dir will b downstream}
T = D{(2x)/(x^2 - y^2).
Solution.
T = (105 *2*9)/(9^2-1.5^2).
T = (1890)/(78.75),
T = 24 Hours.
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