Please turn off your computers……we will play a little game first

The Row Boat Puzzle

The Row Boat Puzzle

• A man rows a boat in a river• The man must row from point A to point B• The water in the river steams in the direction from A

to B, with constant speed• The man rows the boat with constant speed

A B

The Row Boat Puzzle

• Due to the stream, it takes less time to row from A to B, than from B to A

• It takes 6 minutes to row from A to B• It takes 12 minutes to row from B to A• QUESTION: How long will it take to row from A to B,

if there was no stream…?

A B

The Row Boat Puzzle

• Hint #1• Call the speed of the rower R• Call the speed of the stream S• Total speed from A to B: R+S• Total speed from B to A: R-S• Total speed without stream: R

The Row Boat Puzzle

• Hint #2• Distance = Speed x Time• The distance A to B is called L, then:

L = (R + S) x 6 minutesL = (R – S) x 12 minutes

• Find S expressed by R

The Row Boat Puzzle

• Hint #3• S = 1/3 R, so by inserting this:

L = 4/3 R x 6 minutesL = 2/3 R x 12 minutes

• We must then solve L = R x ? minutes