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Mathematics

A boat sails a distance of 44 km in 4 hours with the current. It takes 4 hours 48 minutes longer to cover the same distance against the current. Find the speed of the boat in still water and the speed of the current.

Linear Equations

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Answer

Let speed of boat in still water be x km/h and speed of current be y km/h.

Speed of boat in the current = (x + y) km/h

Speed of boat against current = (x - y) km/h

Given, boat takes 4 hours to go 44 km with the current

44x+y=4\therefore \dfrac{44}{x + y} = 4

⇒ 4(x + y) = 44

⇒ x + y = 11 …….(i)

Given, boat takes 4 hours 48 minutes longer

44xy=4+4+486044xy=4+4+4544xy=20+20+4544xy=445xy=44×544xy=5…….(ii)\therefore \dfrac{44}{x - y} = 4 + 4 + \dfrac{48}{60} \\[1em] \Rightarrow \dfrac{44}{x - y} = 4 + 4 + \dfrac{4}{5} \\[1em] \Rightarrow \dfrac{44}{x - y} = \dfrac{20 + 20 + 4}{5} \\[1em] \Rightarrow \dfrac{44}{x - y} = \dfrac{44}{5} \\[1em] \Rightarrow x - y = \dfrac{44 \times 5}{44} \\[1em] \Rightarrow x - y = 5 …….(ii)

Adding (i) and (ii) we get,

⇒ (x + y) + (x - y) = 11 + 5

⇒ 2x = 16

⇒ x = 8.

Substituting value of x in (i) we get,

⇒ 8 + y = 11

⇒ y = 3.

Hence, speed of boat in still water = 8 km/h and speed of current = 3 km/h.

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