Answer:
Defining Variables:
Let the number of days the snail takes to climb = x days
Total distance climbed in x days = x*4
Total distance slipped in x days = 2*x
Solving for the number of days:
Since the total distance the snail climbs is 20ft (depth of well)
The total distance climbed - total distance slipped = 20
replacing the variables
4x - 2x = 20
2x = 20
x = 10
Therefore, it will take the snail 10 days to reach the top