HELP!!! word problem?

Question

A group of four students wish to cross a bridge without side rails in the middle of the jungle very late at
night. They have one lantern to share. No one may take a step without holding the lantern (it's dark at
night with no moon). No more than two people may be on the bridge at one time, not even for a
moment. When two students walk together, they must move at the rate of the slowest person. What is
the shortest time it would take for all of them to get across? Use the following information to solve the
problem:
• The first student, Joe, can cross the bridge alone in 5 minutes.
• The second student, Torey, can cross the bridge alone in 10 minutes.
• The third student, Sarah, can cross the bridge alone in 20 minutes.
• The fourth student, Mike, can cross the bridge alone in 25 minutes.
my dad asked me this question i thought the answer was 120 mins but he says it isnt wat is the answer

Answer 1

J+T cross, taking 10 minutes
J returns with lantern, taking 5 (15) total
S+M cross, taking 25 minutes (40 ) total
T takes lantern back, 10 minutes (50) total
J+T cross, taking 10 minutes (60) total

Answer 2

1. Joe and Mike across with lantern = 25 minutes
2. Joe returns with lantern = 5 minutes
3. Joe and Sarah across = 20 minutes
4. Joe returns with lantern = 5 minutes
5. Joe and Torey across = 10 minutes

At this point, everyone is across. Total time = 25+5+20+5+10 = 65 minutes

The math would be
# of pairs with fastest (joe) and everyone else = 3 pairs

Each pair travels at slowest time within pair = 25 + 20 + 10 = 55

# of trips alone for joe = 2 (# of pairs - 1, given that with the last pair, he is across as well)

Amount of solo time for Joe = 2 x 5 = 10

Total time = 55 + 10 = 65

Answer 3

Joe and Torey cross time = 10 minutes
Joe returns time = 5 minutes
Joe and Sarah cross time = 20 minutes
joe returns time = 5 minutes
Joe and Mike cross time = 25 minutes
Total time = 10+5+20+5 +25 = 65 minutes

Answer 4

You will use Joe to take every one accross.
Joe & Torey cross in 10 min
Joe returns 5 min
Joe and Sarah cross 20 min
Joe returns 5 min
Joe and Mike cross 25 min
total time 65 min.

Answer 5

There is a logic problem with this question:

1) No more than two people may be on the bridge at one time, not even for a moment.

Although Joe is the quickest he is not able to go back without the individual he walked across the bridge.

Answer 6

how about this, for 1 way of doing it.
Joe crosses w/Mike 1st = 25 min.
Joe goes back to the other side = 5 min.
Joe crosses w/Sarah = 20 min.
Joe goes back to the other side = 5 min.
Joe crosses w/Torey = 10 min.
for a grand total of 65 min.

Answer 7

J + T cross = 10 mins
J returns = 5
J + S cross = 20
J returns = 5
J + M cross = 25

Total 65 minutes

Oops - I missed the idea of sending S + M together - neat !