These are some riddles I cannot figure out the answers to!
Thanks a lot!!

There is a long bridge and it's dark. 4 people have 1 flashlight, and everyone needs to get across. Only 2 can go at a time with the flashlight. one person can run it in 10 minutes. one person can run it in 5 minutes. one person can run it in 2 minutes, and the last person can run it in 1 minute. What is the fastest time they can run it in and how?
(btw, i know the time we're shooting for is 17 minutes)

There is a cube. and its cut up into 27 smaller cubes. so 9 to a face (picture a rubix cube). imagine each cube is like a little room to a house. and there is a door connecting each one. and you are in the exact middle cube. is it possible to travel throught each room without overlapping one? if so, how? if not, why not?
(the doors connect both by the sides and top to bottom)

There are 2 strings. they each burn at a different rate, but eventually it takes 1 hours time to burn them. (but the rate might be very fast for the first half then slow down a ton. etc.) both strings are different rates. How would you measure out 45 minutes?

Hope you can get the answers! thanks!