Flashlight

[rich_m]

Could any one help me with this puzzle:-

There are four people on one side of a river. There is
a bridge crossing the river, but outside is very dark.
While they do have a flashlight, only two people at a
time can cross the bridge and crossing can not be done
without a flashlight. Knowing that they cross the
bridge in 1,2,5 and 10 mins. respectively, can they
cross the bridge in 17 mins? (When two people cross the bridge they cross with the speed of the slowest one).

[CESS.tk]

Let |`-?| be the bridge:

1 2 5 10 |`-?| -> 0 min.
5 10 |`-?| 1 2 -> 2 min.
1 5 10 |`-?| 2 -> 3 min.
1 |`-?| 2 5 10 -> 13 min.
1 2 |`-?| 5 10 -> 15 min.
|`-?| 1 2 5 10 -> 17 min.


The trick is in understanding that 5 and 10 have to cross the bridge simultaneously and only once.

[df]

i did this test as part of a job interview once. hahaha