Question

The speed of a boat in still water is 15km/h and the speed of a stream is 5km/h.Find the time taken by the boat to cover 40km upstream and 36 km downstream​

Answer 1

Answer:

Given:

The speed of a boat in still water is 15 km/h,

And the speed of the current is 5 km/h.

Distance of upstream or downstream = 60km.

Concept used:

If the speed of boat is X km/hr, and the speed of the stream is y km/hr then,

Speed of boat upstream = (X - Y) km/hr.

Speed of boat downstream = (X + Y) km/hr

formula used:

Time = Distance/Time

Calculation:

According to the question:

D/(X - Y) + D/(X + Y) = T

⇒ 60 km/(15 - 5) km/hr + 60 km/(15 + 5 ) km/hr = T

⇒ T = (60/10 + 60/20) hr.

⇒  (6 + 3) hr. = 9 hr.

∴ The time taken by the boat is 9 hours.

Answer 2

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Given:

The speed of a boat in still water is 15 km/h,

And the speed of the current is 5 km/h.

Distance of upstream or downstream = 60km.

Concept used:

If the speed of boat is X km/hr, and the speed of the stream is y km/hr then,

Speed of boat upstream = (X - Y) km/hr.

Speed of boat downstream = (X + Y) km/hr

formula used:

Time = Distance/Time

Calculation:

According to the question:

D/(X - Y) + D/(X + Y) = T

⇒ 60 km/(15 - 5) km/hr + 60 km/(15 + 5 ) km/hr = T

⇒ T = (60/10 + 60/20) hr.

⇒  (6 + 3) hr. = 9 hr.

∴ The time taken by the boat is 9 hours.