A snail fell down a 50 feet deep well it crawls up 5 feet every day and slides down two feet each night. on which day will the snail leave the well

Day Up Down Deep at the end of the day

1 5 2 50 - 3 = 47

2 5 2 50 - 6 = 44

3 50 - 9 = 41

4 50 - 12 = 38

...

15 50 - 15*3 = 5

16 5 5 - 5 = 0 'this day it leaves when goes up 5 feet and so does not go down the 2 feet

The snail will leave on the day 16th