Queston :
There are 4 persons need to cross the bridge.
Unfortunately, they have only one flash light and it has enough light for only 17 minutes.
One can cross the bridge in 1 minute, another in 2 minutes, the third in 5 minutes, and fourth in 10 minutes to cross the bridge.
Only two members can cross the bridge at a time. How could they cross the bridge within 17 minutes?

Side1: 1 min, 2min, 5min, 10min. 
Side2: none 
Totaltime: 0min 

Step1: First send 1 minute and 2 minute guys to another side(takes 2 minutes).    
Side1: 5min, 10min 
Side2: 1min, 2min 
Totaltime: 2min 

Step2: Send back 1min guy to Side1. 
Side1: 1min, 5min, 10min 
Side2: 2min 
Totaltime: 3min

Step3: send 10 minute and 5 minute guys to side2(takes 10 minutes). 
Side1: 1min 
Side2: 10min, 5min, 2min 
Totaltime: 13min 

Step4: Send back 2min guy to Side1. 
Side1: 1min,2min 
Side2: 10min, 5min 
Totaltime: 15min 

Step5: Send 2min guy and 1 min guy to Side2(takes 2min).        
Side1: none        
Side2: 10min, 5min, 1min, 2min     
Totaltime: 17min