How Fast Can Spiderman Get Freedom? | A tricky question

Mathematics questions on speed, velocity or rate can be straight forward or ....tricky.

You need to read the question, understand it, and think carefully about it.

Do not be afraid, though.
It is only applicable for fun or amusement.

I have one here. * Dare to attempt... ? *

Question:

Spiderman fell into a deep and slippery oil tunnel dugg vertically into the ground. To get out into the city, he has to, obviously, climb out of it. However, the tunnel is 20 metres deep, and he can only manage to move up 3 metres per hour due to back injury. But as the wall of the tunnel is too slippery, any attempt to move 3 metres will result in a slip back of 2 metres. This make spiderman's rate of climb to be effectively pegged at 1 metre per hour only. How long will spiderman then take to reach out of the tunnel?

NOTE: It seems like spiderman needs take 20 hours to achieve this feat. This is due to the tunnel height of 20 metres and his rate of upward climb being at 1 metre / hour. This is wrong! The assumption has to be properly thought over. Spiderman will be happy as it will take lesser time for him to reach freedom.

....... think it over, if you surrender and urgently need to see spiderman .......

.

the answer is ==>

Spiderman will be over the edge of the tunnel at the " see below " hours.

Why?

As he can only progress at 1 metre / hour, it meant that at the 2th hour, he will only start at a 2 metre height from bottom. At the 18th hour, he will start at 18 metres from bottom. From there on, he just need to cover another 2 metres to be over the edge of the tunnel (before falling back 2 metres). Therefore he needs only 18 hours plus another 2/3 hour to be happy. Got it?

:D