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 per day (3 feet up during the day, 2 feet back at night). However, on the final day of climbing, it will reach the top and not slip back. So, to climb 20 feet, considering the pattern, it climbs 3 feet on the last day and reaches the top. To climb 17 feet (since 20 - 3 = 17), at a rate of 1 foot per day effectively, it takes 17 days. Then, on the 18th day, it climbs the final 3 feet and reaches the top. Thus, it takes 18 days for the snail to reach the top of the well.