The Collapsing Bridge

 
The Collapsing Bridge

Problem statement:

A bridge will collapse in 17 minutes. 4 people want to cross it before it will collapse. It is a dark night and there is only one torch between them. Only two people can cross at a time.
 
“A” takes a minute to cross.
“B” takes 2 minutes.
“C” takes 5
and “D” takes 10 minutes
 
How do they all cross before the bridge collapses?

Done thinking? Click here to view the solution.

A and B cross first using up 2 minutes.
A comes back making it 3
C and D cross making it 13 minutes
then B crosses back over making it 15 minutes.
And finally A and B cross together to make it 17 minutes!