A worm is at the bottom of a 12- foot wall. Every day it crawls up 3 feet, but at night it slips down 2 feet. How many days does it take the worm to reach the top of the wall?
It rises a net distance of 1 feet per day. After nine days it has risen nine feet. What happens on the tenth day?
Eleven days.
To determine how many days it takes for the worm to reach the top of the wall, you need to calculate the "net progress" each day. The net progress is the difference between the distance the worm climbs during the day and the distance it slips down during the night.
In this case, the worm climbs 3 feet during the day and slides down 2 feet at night. Therefore, the net progress can be calculated as:
3 feet climbed - 2 feet slid down = 1 foot of net progress per day
Since the wall is 12 feet tall, the worm needs to make a net progress of 12 feet to reach the top. By dividing the total distance (12 feet) by the net progress per day (1 foot), you can find out how many days it takes:
12 feet / 1 foot per day = 12 days
So, it takes the worm 12 days to crawl to the top of the wall.