A family must catch a train on the other side of a river.
The train is leaving in 30 minutes.
They have been joined by their friend, a cop,
who want to help them cross the river.
1) The cop can cross the river in 1 minute.
2) Father can cross in 3 minutes.
3) Mother can cross in 6 minutes.
4) Daughter can cross in 8 minutes.
5) Son can cross in 12 minutes.
6) If two people are on the raft, they will cross the river in the time that it would take for the slower person to cross alone.
Can you help the family catch their train?