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Crossing a bridge

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Four soldiers must cross a bridge and they know the enemy is not far behind. Only up to two can safely walk on the bridge at any time. There's only one flashlight among them, and it is necessary to use the flashlight to see while crossing.

The soldiers have various injuries and can only cross the bridge so fast.

The following are the fastest times that each can cross:

MSGT Moore: 1 minute

1LT Jackson: 2 minutes

PFC Diggs: 5 minutes

CPT Pruden: 10 minutes

What is the fastest time they can achieve in all safely crossing the bridge?

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Guest

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Very good question.

Here is my answer, ( i hope i'm not 100% wrong ):

1. CPT Pruden and MSGT Moore cross the bridge first = 10 mins

2. MSGT Moore crosses back = 1 min

3. MSGT Moore and PFC Diggs cross = 5 mins

4. MSGT Moore crosses back = 1 min

5. MSGT Moore and Jackson cross = 2 min

TOTAL = 19 mins.

Anybody corssed them faster?

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is this it?

1. MSGT Moore and 1LT Jackson = 2 mins

2. MSGT Moore crosses back = 1 min

3. PFC Diggs and CPT Pruden = 10 mins

4. 1LT Jacksion crosses back = 2 mins

5. MSGT Moore and 1LT Jackson cross = 2 min

TOTAL = 17 mins.

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Nice job!

Answer is 12 minutes

Step 1 : Let the 10 mins guy start crossing...

Step 2 : After 5 minutes, let the 5 minute guy start..they reach the end at the same time

Step3 : Let the 2 minutes guy start

Step 4 : After a minute, let the one minute guy start...they reach at the same time..so in total 12 minutes

Glenn

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Answer is 12 minutes

Step 1 : Let the 10 mins guy start crossing...

Step 2 : After 5 minutes, let the 5 minute guy start..they reach the end at the same time

Step3 : Let the 2 minutes guy start

Step 4 : After a minute, let the one minute guy start...they reach at the same time..so in total 12 minutes

Glenn

The only problem with your solution is the flashlight,they can't cross without light.That's why your solution doesn't work.The fastest time is 17min.

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I'm getting 14 minutes.

The problem said 'up to' 2 men can cross at the same time.

CPT Pruden(10 minutes) and PFC Diggs(5 minutes) cross with the flashlight = 10 minutes

MSGT Moore(1 minute) crosses by himself and gets the flashlight = 1 minute

MSGT Moore(1 minute) comes back with the flashlight = 1 minute

1LT Jackson(2 minutes) and MSGT Moore(1 minute) cross = 2 minutes

= 14 minutes.

Let me know if I missed something.

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If only two could cross at once with out the flashlight then you are off by 2 whole minutes...so 12 minutes would be the fastest

"MSGT Moore(1 minute) crosses by himself and gets the flashlight = 1 minute

MSGT Moore(1 minute) comes back with the flashlight = 1 minute"

Unnecessary trips if you only can cross 2 at a time without the flashlight, BUT, you need the flashlight to cross so MSGT Moore can not cross over to get the flashlight without the flashlight and then come back for 1LT Jackson...

Edited by finance_it
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Let me know if I missed something.

Step two:

MSGT Moore(1 minute) crosses by himself and gets the flashlight

He can't cross over to get the flashlight because he can't cross without having it.

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Moore 1 minute

Jackson 2 minutes

Diggs 5 minutes

Pruden 10 minutes.

Pruden holding the flashlight to guide the others across, sets off immediately that Jackson, 1 minute behind Moore, arrives the other side. He [Pruden] has had only 2 minute delay [2 men at a time on the bridge] before starting his 10 minute transit. Total time of completion 12 minutes.

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Moore 1 minute

Jackson 2 minutes

Diggs 5 minutes

Pruden 10 minutes.

Pruden holding the flashlight to guide the others across, sets off immediately that Jackson, 1 minute behind Moore, arrives the other side.

Huh?

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Very good question.

Here is my answer, ( i hope i'm not 100% wrong ):

1. CPT Pruden and MSGT Moore cross the bridge first = 10 mins

2. MSGT Moore crosses back = 1 min

3. MSGT Moore and PFC Diggs cross = 5 mins

4. MSGT Moore crosses back = 1 min

5. MSGT Moore and Jackson cross = 2 min

TOTAL = 19 mins.

Anybody corssed them faster?

Here is a faster way...

1 and 2 min men go over first = 2 mins

2 min man goes back = 4 mins

10 and 5 min men go over = 14 mins

1 min man back = 15 mins

1 and 2 min men back again = 17 mins all in.

I can not think of any faster way but there might be one.

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Huh?

Moore and Jackson start across, (2 men at a time), Jackson still has 1 minute to complete when Diggs proceeds (2 men at a time), Diggs still has four minutes to complete when Pruden proceeds ( 2 men at a time).

The bridge is not long, (Moore takes 1 minute), Pruden being last holds the torch in front of himself for the others,he only has to wait until Jackson completes the crossing (2 minutes) before he , Pruden, starts his ten minute crossing. Time elapsed for all four crossing ----12 minutes.

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akaslickster Grand Master

akaslickster

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Four soldiers must cross a bridge and they know the enemy is not far behind. Only up to two can safely walk on the bridge at any time. There's only one flashlight among them, and it is necessary to use the flashlight to see while crossing.

The soldiers have various injuries and can only cross the bridge so fast.

The following are the fastest times that each can cross:

MSGT Moore: 1 minute

1LT Jackson: 2 minutes

PFC Diggs: 5 minutes

CPT Pruden: 10 minutes

What is the fastest time they can achieve in all safely crossing the bridge?

18minutes , but not all at the same time.
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Four soldiers must cross a bridge and they know the enemy is not far behind. Only up to two can safely walk on the bridge at any time. There's only one flashlight among them, and it is necessary to use the flashlight to see while crossing.

The soldiers have various injuries and can only cross the bridge so fast.

The following are the fastest times that each can cross:

MSGT Moore: 1 minute

1LT Jackson: 2 minutes

PFC Diggs: 5 minutes

CPT Pruden: 10 minutes

What is the fastest time they can achieve in all safely crossing the bridge?

The riddle suggests that only two people can walk on the bridge at the same time. Given that information, I would suggest that the fastest crossing time for the four soldiers is 2 minutes.

MSGT Moore carries CPT Pruden, while 1LT Jackson carries PFC Diggs.

It might take a bit longer than the 2 minutes that 1LT Jackson would take had he crossed without such a burden, but it would certainly be faster than the 17 minutes suggested.

Cheers,

Gabe

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Moore and Jackson start across, (2 men at a time), Jackson still has 1 minute to complete when Diggs proceeds (2 men at a time)

Jackson can't complete the crossing without Moore; the flashlight is needed to cross. Diggs also can't begin to cross without the flashlight.

The riddle suggests that only two people can walk on the bridge at the same time.

No, the riddle says that only two can safely walk on the bridge at at any time, and that suggests that the bridge won't be any safer if four people are on the bridge just because two aren't actually walking. Nice try though. :)

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Does this work?

1) MSGT Moore & CPT Pruden (CPT Pruden has flashlight)

when MSGT Moore gets to other end

2) 1LT Jackson starts to walk across

When 1LT Jackson gets to other end

3) PFC Diggs starts to walk across

Since CPT Pruden, the slowest, has the flashlight they would be able to see the light when crossing, therefore crossing in 10 minutes

is this correct?

Edited by Martini
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