Monks and Cannibals

Difficulty:
★★☆☆☆

Problem:

Three monks and three cannibals are trying to cross a river. In front of them is a boat that can fit two. The monks are safe as long as there are at least as many monks as cannibals on both sides of the river, but if there are more cannibals than monks on either side of the river, the cannibals will eat the monks. How can they all cross the river while making sure that no monks get eaten?

Solution:

Cryptarithm: Half + Fifth + Tenth + Tenth + Tenth = Whole

Difficulty:
★★★★☆

Problem:

Figure out which digit each letter represents. Every letter is a different digit and there are no leading zeros.

    H A L F
  F I F T H
  T E N T H
  T E N T H
+ T E N T H
------------
  W H O L E



Solution:

Black and White Hats

Difficulty:
★★☆☆☆

Problem:

Alice, Bob, and Cathy have a box that contains three black hats and two white hats. They each close their eyes, take out a hat from a box and put it on. They close the box and open their eyes, so that they can see the color of the hats that the other two are wearing but they cannot see their own.

Alice says, "I don't know the color of my hat."

Bob says, "I don't know the color of my hat."

Cathy says, "I know the color of my hat."

What color is Cathy's hat?


Solution: