Snail in a Well

Brain Teasers

Classic Puzzles

Easy

A snail climbs

3

meters each day and slides down

2

meters each night. On which day does it leave a

10

-meter well?

Hint 1

The snail escapes during a day climb, before sliding back.

Hint 2

Net progress is $1$ meter per full day.

Show worked solution

1. Before the last day
After $7$ full days and nights it is at $7$ meters.
2. Last climb
On day $8$ it climbs $3$ meters to $10$ and is out.
3. Key idea
Treat the final step separately; naive division ( $10/1 = 10$ ) is the trap.

Answer: 8

1. Before the last day