Solutions

The cannonball in the boat displaces an amount of water equal to the MASS of the cannonball. The cannonball in the water displaces an amount of water equal to the VOLUME of the cannonball. Water is unable to support the level of salinity it would take to make it as dense as a cannonball, […]

The monkey is pulling down on the rope hard enough to pull itself up. This increases the tension in the rope just enough to cause the weight to rise at the same rate as the monkey, since they are of equal mass.

The wiseman tells them to switch camels.

Mirrors invert front to back, not left to right.
The popular misconception of the inversion is caused by the fact that a person when looking at another person expects him/her to face her/him, so with the left-hand side to the right. When facing oneself (in the mirror) one sees an ‘uninverted’ person.
See Martin Gardner, “Hexaflexagons and […]

Mr. Smith asked nine persons, who replied him different numbers. The highest number could be 8, because everybody of the 10 participants knows at least himself and his/her partner.
If the highest number of 9 different numbers is 8, this means, that the answers were: 0, 1, 2, …, 8.
Let’s call the nine persons after the […]

Here is the solution.
- Attach a lock to the ring. Send it to her.
- She attaches her own lock and sends it back. You remove your lock and send it back to her.
- She removes her lock.

This answer did not satisfy Don Kirkham, who has a more elegant solution:

‘I am an instructor at […]

Take the chicken first and come back.
Get the grain, take it accross and take the chicken back with you.
Leave the chicken and take the fox and come back.
Get the chicken…
Lets get visual:
C = chicken
G = Grain
F = fox
} = one side of river{ = other side of river.

C G F […]

Because of buoyancy, the helium balloon on the string will want to move in the direction opposite the effective gravitational field existing in the car.
Thus, when the car turns the corner, the balloon will deflect towards the inside of the turn.

Gravity from another perspective …

A so-called ‘Nobody‘ has sent in the following on this:

‘The answer […]

First the two women cross the river together (10 min). Then the quick woman (5) returns (+5=15).

Now the two men cross the river (+25=40). The other woman (10) returns with the boat (+10=50).
Now both women take their last journey to be re-united with their men … (+10=60).

YES ! You made it, they have crossed the […]