Crossing the bridge.

4 people have to cross the bridge: Child, Father, Uncle, Grandpa.All they have is a single flashlight and for some reason they know thatthe batteries will last for exactly 60 minutes.
It is also quite foggy, the beam of the flashlight cannot be seen for more than a few meters - the bridge is far longer.The bridge can carry only two persons at a time - strange enough, it depends only on the *number*, not on the *weight* of the people.

However, each person takes a different amount of time to cross the bridge:
Child: 5 min
Father: 10 min
Uncle: 20 min
Grandpa: 25 min
In what order do they have to cross the bridge so that nobody is on the bridge in the dark - *and* the flashlight doesn't burn out before they all reached the other side?

Answer:
All people are on BankA and they want to reach BankB.
1)Child and Father cross the bridge from BankA to BankB(10 min)
2)Child returns to BankA(5 min)
3)Uncle and Grandpa cross the bridge from BankA to BankB(25 min)
4)Father returns to BankA (10 min)
5)Child and Father cross the bridge from BankA to BankB(10 min)

Total Time consumed is: 10+5+25+10+10 = 60 min.