Mate No Matter What

If White is to play, can he always mate Black in 2 moves, regardless of the moves played before?

The first thing to notice is that since the last move was made by Black, either the king or the rook was moved and therefore Black cannot castle anymore. Now White plays Qa1 and no matter what is Black’s next move, Qh8 gives check-mate.

Chase on a Horse’s Back

You are chasing a thief on the back of a horse on a (ruined) chessboard. You must traverse the maze by using only knight’s movements, but be careful – pieces can destroy each other.

The solution is shown below.

Ping Pong Ball

Your last ping pong ball falls down into a narrow pipe embedded in concrete one foot deep. How can you get it out undamaged if all you have is your tennis paddle, your your shoe-laces, keys, wallet and a plastic water bottle, which does not fit into the pipe?

Using the plastic bottle, pour water into the pipe so that the ball will rise up.

Puzzle Sum 1

What two animals do these sums spell?

BABY – Y + MOON – M = BABOON
DON + KEY = DONKEY

Running Dog

Two people – Mick and Goof, 100 meters apart, start walking towards each other with constant speeds of 2m/s. At the same time Mick’s dog starts running back and fourth between them with constant speed of 6m/s until Mick and Goof meet. How much distance does the dog cover in total?

Mick and Goof will meet after 100/(2 + 2) = 25 seconds. Therefore the dog will run for 25 seconds and will cover 6 x 25 = 150 meters in total.

Her Name

Mary’s father has 4 children. Their names are April, May, June and ???

Mary.

Grasshoppers

Four grasshoppers start at the ends of a square in the plane. Every second one of them jumps over another one and lands on its other side at the same distance. Can the grasshoppers after finitely many jumps end up at the vertices of a bigger square?

The answer is NO. In order to show this, assume they can and consider their reverse movement. Now the grasshoppers start at the vertices of some square, say with unit length sides, and end up at the vertices of a smaller square. Create a lattice in the plane using the starting unit square. It is easy to see that the grasshoppers at all times will land on vertices of this lattice. However, it is easy to see that every square with vertices coinciding with the lattice’s vertices has sides of length at least one. Therefore the assumption is wrong.

Missionaries, Cannibals

Three missionaries and three cannibals must cross a river with a boat which can carry at most two people at a time. However, if on one of the two banks of the river the missionaries get outnumbered by the cannibals, they will get eaten. How can all 6 men cross the river without anybody gets eaten?

Remark: The boat cannot cross the river with no people on board.

Label the missionaries M1, M2, M3 and the cannibals C1, C2, C3. Then:

1. M1 and C1 cross the river, M1 comes back.
2. C2 and C3 cross the river, C2 comes back.
3. M1 and M2 cross the river, M1 and C1 come back.
4. M1 and M3 cross the river, C3 comes back.
5. C1 and C2 cross the river, C1 comes back.
6. C1 and C3 cross the river.

Now, everyone is on the other side.

Friends and Enemies

Show that in each group of 6 people, there are either 3 who know each other, or 3 who do not know each other.

Let’s call the people A, B, C, D, E, F. Person A either knows at least 3 among B, C, D, E, F, or does not know at least 3 among B, C, D, E, F.

Assume the first possibility – A knows B, C, D. If B and C know each other, C and D know each other, or B and D know each other, then we find a group of 3 people who know each other. Otherwise, B, C, and D form a group in which no-one knows the others.

If A doesn’t know at least 3 among B, C, D, E, F, the arguments are the same.

Fathers, Sons, and Fish

Two fathers and two sons went out fishing. Each of them catches two fish. However, they brought home only six fish. How so?

They were a son, his father, and his grandfather – 3 people in total.