Yesterday's:
There are eight mints. They are all the same size and color. One mint weighs slightly more than the others and it is poisonous. You have a balanced scale and can only use it twice. How can you find the poisoned mint?
Take any six mints and divide them into two groups. Weigh them against each other. If they weigh the same, the poisonous mint is one of the other two and you can weigh them against each other to find the poisonous one.
If one of the two groups of three is heavier than the other, take two of the mints and weigh them against each other. If the weigh the same, the third mint is the poisonous one.
As to LPWH....John, you've got it!
<marquee direction=left>L P WH </marquee>