Four People And The Bridge

Four people must cross a rickety bridge at night.

Unfortunately, they have only one torch and the bridge is too dangerous to cross without one.

The bridge can only hold two of them at a time.

The four people cross at different speeds: Times for each person: 1 minute, 2 minutes, 7 minutes and 10 minutes.

What is the shortest time in which they can all cross?

Ah! Click here to read the solution.

1 and 2 minute-person cross first

2 minute-person comes back

7 and 10 minute-person go across the bridge

1 minute-person comes back

Finally, 1 and 2 minute-person cross the bridge (voilà)

Total time (shortest) = 2 + 2 + 10 + 1 + 2 = 17 mins. 🙂

The Farmer, The Fox And The Chicken

A farmer is standing on one bank of a river, with a fox, a chicken, and a bag of grain.

He needs to get to the other side of the river, taking the fox, the chicken, and the grain with him.

However, the boat used to cross the river is only large enough to carry the farmer and one of the things he needs to take with him, so he will need to make several trips in order to get everything across.

In addition, he cannot leave the fox unattended with the chicken, or else the fox will eat the chicken; and he cannot leave the chicken unattended with the grain, or else the chicken will eat the grain.

The fox is not particularly partial to grain and may be left alone with it.

How can the farmer get everything across the river without anything being eaten?

Ah! Click here to read the solution.

1. The farmer takes the chicken across first, leaving the fox and grain together on the other side.

2. He returns and gets the fox, but when he deposits the fox on the other side, he takes the chicken back across, so that the fox and chicken are not left alone together.

3.He drops the chicken off, picks up the grain, and takes it across to deposit with the fox.

4. Finally, he returns to retrieve the chicken and takes it to the other side. At no time are the fox and chicken left alone together, nor are the chicken and grain. 🙂