Crossing the Bridge

Alice, Bob, Carrie, and Dan have to cross a rickety bridge. The bridge can only hold two people at a time. They also have a flashlight, and one person on the bridge must be always holding the flashlight. Alice can cross the bridge in 1 minute, Bob can cross the bridge in 2 minutes, Carrie can cross the bridge in 5 minutes, and Dan can cross the bridge in 10 minutes. What is the fastest amount of time that all four of them can cross the bridge?

• This problem has no tricks, no one is carrying another person, dragging them, running, etc.

• There is a good answer and a best answer

• You are as fast as the slowest person on the bridge