Riddle: In a contest, there are four fruits (an apple, a banana, an orange, and a pear) which have been placed in four closed boxes (one fruit per box). People may guess which fruit is in which box. There were 123 participants in the contest. The results are; 43 people guessed none correctly, 39 people guessed one correctly and 31 people have guessed two correctly. How many people guessed three correctly and how many people guessed all four correctly?
Answer: It is not possible to only get three correct because the fourth would also be correct. Therefore, the answer would be (123-43-39-31 = 10) 10 people guessed all four correctly.