### Brain Teasers

# A New Twist on an Old Favourite

Walter, Xavier, Yoshi, and Zeke crossed a river in a tiny rowboat. They all started on the same side of the river. They made three trips from the starting side to the destination side, and two trips from the destination side to the starting side. Here are some facts:

1. On each trip from the starting side of the river to the destination side, two people were in the boat, but only one person rowed the boat, and that person rowed the boat for the entire trip.

2. On each return trip, only one person was in the boat.

3. Walter is the weakest of the group. He could only row the boat if no one else is in it.

4. Xavier is the second weakest of the group. He can only row the boat if he is by himself or if Yoshi, the lightest of the group, is a passenger.

5. Each man rowed the boat at least once.

Who rowed twice?

1. On each trip from the starting side of the river to the destination side, two people were in the boat, but only one person rowed the boat, and that person rowed the boat for the entire trip.

2. On each return trip, only one person was in the boat.

3. Walter is the weakest of the group. He could only row the boat if no one else is in it.

4. Xavier is the second weakest of the group. He can only row the boat if he is by himself or if Yoshi, the lightest of the group, is a passenger.

5. Each man rowed the boat at least once.

Who rowed twice?

### Answer

Yoshi rowed twice.Fact 5 tells us that Walter had to row the boat at least once, but fact 3 tells us that he had to go by himself. This means he could only row the boat on a return trip, which means he rowed on at least one return trip.

The man who rowed twice could not have rowed on two trips from the starting side to the destination side, because he would have had to make a third trip by himself back to the starting side. So the man who rowed twice must have made a return trip at least once.

Now we know that if Walter made two trips, they must both have been return trips, and Xavier, Yoshi, and Zeke each rowed for one of the other three trips. If Walter made only one trip, the other person who made a return trip must have been the person who rowed twice (Xavier, Yoshi, or Zeke) and that person would also have made one of the other three trips. So the three trips from the starting side to the destination side must have been rowed by Xavier, Yoshi, and Zeke.

Fact 1 tells us that Xavier's trip to the destination side must have had a passenger, and fact 4 tells us that that passenger must have been Yoshi. Yoshi would have had to row back to row his trip to the destination side, or else Yoshi rowed to the destination side, then back to the start, then got rowed across by Xavier.

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