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Here's one:

A young boy, a teenage girl, a middle-age lady and an old man are standing on one side of a bridge at night.  The bridge can only hold two people at a time, and they only have one lamp by which to see.  They can't cross the bridge without the lamp.  Their speeds crossing the bridge are:

Young Boy: 2 minutes
Teen Girl: 1 minute
Lady: 5 minutes
Old Man: 10 minutes

At the other side of the bridge is a landing where they all can stand safely.  From that landing, there's a narrow path that goes down to a huge river below the bridge.  Again, only two of them can walk the path at a time, and they cannot walk it without the lamp.  Their times going down and back up the path are as follows:

Young Boy - Down: 1 minute  Up: 4 minutes (he has short legs)
Teen Girl - Down: 2 minutes  Up: 3 minutes
Lady - Down: 4 minutes  Up: 2 minutes
Old Man - Down: 10 minutes  Up: 25 minutes

Question:
What's the fastest possible way for them all to reach the river? 

This one has already been posted here some times - in another version...
But still, it is good.

S.H. wrote:

Spoiler:

17+21 = 38mins?
By the way, it's LT XIX

Nope!  There's a faster way. 

Oh, and oops! on the roman numerals.  Just fixed it.

akai-kun wrote: This one has already been posted here some times - in another version...
But still, it is good.

Ahh... It may seem so, but has it? 

This good, seeing the Lateral Thinking continueing, thanks! Thinking about it.

The one you´re saying is Lateral Thinking V. That one caused some headaches...

Okay, time for a hint:

What is the fastest possible way for them all to reach the river?

Fastest way : Using the force of gravity to go down the river by jumping?  (just a joke)

S.H. wrote: Fastest way : Using the force of gravity to go down the river by jumping?  (just a joke)

Pin Pon!  That's the right answer!!!  They all jump off the bridge.   
And I'm not joking either!  After all, this *is* a lateral thinking question, not a math question.