Snow White offered the Seven Dwarfs a weighing machine. One after the other, they went on the machine and they wrote their weights on a piece of paper. Then they gave it to Snow White, but without writing their names:
Feeling playful, they also went two by two on the machine. Except Grumpy, who didn't want to join the fun, obviously. Once they were done, they tell Snow White that:
Doc and Sneezy were on the machine at the same time;
Dopey and Happy were too;
Bashful and Sleepy were the last two dwarfs to go together on the machine.
Altogether, they say to Snow White that the weight shown was the same each time. Snow White then says: "Don't tell me anything more, I know how much Grumpy weighs."
And you, do you know how much Grumpy weighs?