Microsoft has such a recruitment tests: One night, four members of a chorus must arrive at the concert venue in the shortest time, and they must pass the customs on the way.

According to the minimum time required for four people to cross the bridge, it can be concluded that the two people who use the least time will cross the bridge first, which will save them time to send lights back and forth.

So: (1) 1 2 minutes to cross the bridge first (it takes 2 minutes at this time).

(2) 1 minute back, (at this time, * * * takes 3 minutes).

(3) Crossing the bridge for 5 minutes 10 minutes (* * * takes 2+ 1+ 10= 13 minutes).

(4) Come back in 2 minutes (* * * takes 2+1+10+2 =15 minutes).

(5) 1 minute 2 minutes to cross the bridge (* * * takes 2+1+10+2 =17 minutes).

At this time, it takes 17 minutes to completely cross the bridge.

Answer: It takes at least 17 minutes for all four people to cross the river.