solution for question 1

On the first day, the snail reaches a height of 5 meters and slides down 4 meters at night, and thus ends at a height of 1 meter. On the second day, he reaches 6 m., but slides back to 2 m. On the third day, he reaches 7 m., and slides back to 3 m. ... On the fifteenth day, he reaches 19 m., and slides back to 15 m. On the sixteenth day, he reaches 20 m., so now he is at the top of the pit! Conclusion: The snail reaches the top of the pit on the 16th day!... .