A man rows upstream in still water at 3 km/h and back to the same place at 5 km/h; he takes 48 minutes altogether. How far upstream did he go?
Answers
Answered by
14
Given :-
- A man rows upstream in still water at 3 km/h and back to the same place at 5 km/h; he takes 48 minutes altogether.
To Find :-
- How far upstream did he go
Answer :-
Let the distance of upstream x km.
As we know that,
- Time = Distance ÷ Speed
Therefore,
- Time taken to go upstream = x ÷ 3 hours.
- Time taken to go downstream = x ÷ 5 hours.
- Total time = 48 minutes = 48 ÷ 60 hrs = 4 ÷ 5 hrs
According to Question :
→ (x/3) + (x/5) = 4/5
→ 5x + 3x/15 = 4/5
→ 8x/15 = 4/5
→ (8x)(5) = (4)(15)
→ 40x = 60
→ x = 60 ÷ 40
→ x = 6 ÷ 4
→ x = 1.5 km/hr
Therefore,the man went 1.5 km upstream.
Answered by
1
Answer:
Distance travelled upstream = 1.5 km
◆ Explanation -
Let s be the distance man go to. Also vm amd vr be velocity of man and that of riverstream respectively.
During upstream journey,
t1 = s / (vm-vr)
t1 = s / 3
During downstream journey,
t2 = s / (vm+vr)
t2 = s / 5
Total time taken is 48 min,
t = t1 + t2
0.8 = s/3 + s/5
0.8 = s × (3+5)/(5×3)
s = 1.5 km
Therefore, the man went 1.5 km upstream.
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