Question

6) A boat traveled 80 miles downstream and back. The trip downstream took 5 hours. The trip back took

10 hours. What is the speed of the boat in still water? What is the speed of the current?

Answer 1

• 12 mph and 4 mph

Explanation:

• Let the speed of the boat = b and the speed of the current = c

Equations to reflect time, time = distance/speed:

• Downstream

• 80/(b + c)= 5 ⇒ b - c = 80/5 ⇒ b + c = 16

• Upstream

• 80/(b - c) = 10 ⇒ b - c = 80/10 ⇒ b - c = 8

Sum of the 2 equations above

• b + c + b - c = 16 + 8
• 2b = 24
• b = 12
• c = 16 - 12 = 4

So the speed of the boat is 12 mph

The speed of the current is 4 mph