Problem 1. Children visited the dolphinarium. Katya remembered that there were exactly 7 either otters or seals; Yura that there were exactly 6 either sea lions or seals; Igor - that there were exactly 5 either otters or sea lions; Seryozha - that there were the fewest either seals or otters. No one was wrong. How many otters, seals, and sea lions were there in the dolphinarium?

[4 points] (T. Kazitsyna)
Answer: 5 otters, 7 seals, 6 sea lions.

Solution: Since none of the children made a mistake, one of the otters, sea lions, and seals was exactly 5, one was exactly 6, and one was exactly 7. Sergey remembered that the fewest (meaning 5) were either seals or otters, and Igor remembered that 5 were either otters or sea lions. Therefore, 5 were exactly otters. Then 7 were not otters, but seals. Therefore, 6 were sea lions.