From Gerald Lynton Kaufman’s The Book of Modern Puzzles (1954):

1. All DROONS are the same size and shape.
2. All green SLACKENS are the same size and shape.
3. Twenty DROONS just fill up a MULDRUFF.
4. All WALLAXES contain green SLACKENS.
5. A green SLACKEN is 10% bigger than a DROON.
6. A WALLAX is smaller than a MULDRUFF.

“If all MULDRUFFS and all WALLAXES are predominantly RED throughout, what is the largest possible number of green SLACKENS in a WALLAX?”