Snail climbing out of a well – Mathematical interview puzzle – A snail is at the bottom of a 30 foot well. Every hour the snail is able to climb up 3 feet and then it slides back down 2 feet. How many hours does it take for the snail to get out of the well?
Solution: To solve snail climbing puzzle we need to focus on two points.
Since, in 1 hour snail climbs 3 feet and slides down 2 feet. Hence, Snail is covering 3 feet – 2 feet = 1 feet every hour.
Once snail reached at the top it would not slide back. So, the position from where it will reach the top in 1 hour would be 30 feet (depth of well) – 3 feet (up distance covered in 1 hr) = 27th feet. Means, snail will not slide down when it start climbing from 27th feet.
Hence, as a result
As every hour snail is able to climbs 1 feet, it will climb 27 feet in 27 hours.
And last 3 feet it will cover in 1 hour from 27th position.
Hence, time taken to get out of well is: 27 hour+ 1hour = 28 hours.
Answer = 28 hours.