Snail Up The Wall

A snail creeps 10 feet up a wall during the daytime, then falls asleep. It wakes up the next morning and discovers it slipped down 6 feet. If this happens each day, how many days will it take to reach the top of a 20 feet wall?

Escape to answer! 

Source 

A Snail On Top of The Wall !

Read the question first! 

Let's find out progress of snail day by day.

Day 1 : UP to 10, DOWN to 4

Day 2 : UP to 14, DOWN to 8

Day 3 : UP to 18, DOWN to 12

Day 4 : UP to 22 which is greater than 20.

So snail requires 4 days to reach the top of the wall.