A man takes 20 min to row 12km upstream which is a third more than the time he takes on his way downstream what is speed of still water
Answers
Answer:
A man takes 20 min to row 12km upstream which is a third more than the time he takes on his way downstream .The speed of still water is 42 km/hr
Explanation:
Let the speed in still water = x km/hr.
Takes 20 min. to row 12 km upstream
⇒ speed of upstream = 36 km/hr
Time taken for u/s is 1/3 more than for downstream.
Therefore, distance covered in downstream will be 1/3 more.
Hence distance covered by man for downstream in 20 min.
= 12 × (12/3)
= 16km.
So speed of downstream = 48 km/hr.
x + y = 48 and x – y = 36
⇒ x = 42 km/hr.
Answer:45 km/hr
Explanation:Let the speed in still water = x km/hr
Let the speed in downstream =x km/hr
Downstream speed = x+y
Upstream = x-y
:. Upstream Speed = 12/x-y = 20/60
= x-y = 36......... 1️⃣
:. x= y+ 36
Downstream Time = 20-20/3 = 40 / 3 mins
:. Downstream speed = 12/x+y = 40 / 3 × 60
= 12/x+y = 2/9
By crosss multiplication method ...
= 108 = 2x + 2y
= 108 = 2(y+36) + 2y
= 108 = 4y + 72
= 4y = 108 -72
= y = 9
:. x = 9 + 36
= 45 km / hr ...
:. The speed of the boat in still water is 45 km / hr .