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
The snail effectively climbs 1 foot each day. However, on the day it reaches or surpasses the 20-foot mark, it won't slip back. It needs 18 days to climb 18 feet (since 18 days * 1 foot/day = 18 feet), and on the 18th day, when it climbs its 3 feet, it will reach 20 feet and not slip back, so it takes 18 days to reach the top.