4 friends (A,B,C,D) want to cross a bridge.
The bridge is unstable so only one or two people can cross at a time.
They must carry a torch because it is dark.
They only have one torch to use.
They all cross the bridge at different speeds.
If two people cross at the same time they go as fast as the slowest person.

A takes 2 minutes to cross alone.
B takes 3 minutes to cross alone.
C takes 8 minutes to cross alone.
D takes 10 minutes to cross alone.
Question: What is the fastest time that all 4 friends can cross the bridge?