Distance = speed/time

Question

It took Jacob three hours to take his boat to meet his friends travelling with a current of 3 nautical miles per hour. The return trip took him 4 hours. What is the speed of the boat in calm water? What was the distance of a one way trip?

 

 

Needs to use a table 

Answer 1

Distance = rate*time

d = rt

 

Letting b = speed of boat in still water:

 

d = 3(b+3)  moving with the current

d = 4(b-3)   moving against the current

 

Since the distance is the same we can set these equal to each other:

 

3(b+3) = 4(b-3)   clear the parenthesis by multiplying through

3b+9 = 4b-12      subtract 3b from both sides

9 = b - 12            add 12 to both sides

21 = b

 

The boat moves at 21 mph

 

d = 3(b+3) = 3(21+3)=3(24) = 72 miles

d = 4(b-3) = 4(21-3) = 4(18) = 72 miles

 

The one way distance is 72 miles