A bamboo pole has seven knots. A snail got up from the ground. It climbs three knots during the day and descends two knots at night. So, how many days will it take this snail to climb to the top?

Answer and analysis:

Analysis: The snail climbed 3 knots on the first day and slipped down 2 knots, that is, actually climbed 1 knots, climbed 1 knots the next day, climbed 1 knots every day, climbed to the fourth quarter on the fourth day, and climbed 3 knots during the day on the fifth day. When it reached the top of the pole, it was not necessary to slide down at night! So the snail can climb to the top of the pole in five days.