A snail is at the bottom of a 20-foot well. Each day, it climbs up 3 feet, but at night, it slips back 2 feet. How many days will it take for the snail to reach the top of the well?
Correct: A
To solve this, consider the net progress the snail makes each day. The snail climbs 3 feet but slips back 2 feet, resulting in a net gain of 1 foot per day. However, on the final day of climbing, the snail will reach the top and not slip back. The well is 20 feet deep. If we subtract the final climb (3 feet) from the well depth, we get 20 - 3 = 17 feet that the snail must cover with its net daily progress of 1 foot. Thus, it takes 17 days to climb 17 feet (since the snail moves 1 foot net per day), and on the 18th day, the snail climbs the final 3 feet and reaches the top without slipping back. So, it takes 18 days in total for the snail to reach the top of the well.