* They have only one torch and the river is too risky to cross without the torch.

* If all people cross simultaneously then Torchlight won't be sufficient.

* Speed of each person of crossing the river is different.cross time for each person is 1 min, 2 minutes, 7 minutes and 10 minutes.

What is the shortest time needed for all four of them to cross the river?

* They have only one torch and the river is too risky to cross without the torch.

* If all people cross simultaneously then Torchlight won't be sufficient.

* Speed of each person of crossing the river is different.cross time for each person is 1 min, 2 minutes, 7 minutes and 10 minutes.

What is the shortest time needed for all four of them to cross the river?

* They have only one torch and the river is too risky to cross without the torch.

* If all people cross simultaneously then Torchlight won't be sufficient.

* Speed of each person of crossing the river is different.cross time for each person is 1 min, 2 minutes, 7 minutes and 10 minutes.

What is the shortest time needed for all four of them to cross the river?