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Friday, February 9, 2007

Four people need to cross a rickety rope bridge to get back to their camp at night

Four people need to cross a rickety rope bridge to get back to their camp at night. Unfortunately, they only have one flashlight and it only has enough light left for seventeen minutes. The bridge is too dangerous to cross without a flashlight, and it’s only strong enough to support two people at any given time. Each of the campers walks at a different speed. One can cross the bridge in 1 minute, another in 2 minutes, the third in 5 minutes, and the slow poke takes 10 minutes to cross. How do the campers make it across in 17 minutes?
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4 comments:

  1. ChuckFebruary 25, 2007 at 10:17 AM

    First have the 1 minute and 2 minute person cross together with the flashlight. You have used 2 minutes.

    Now have the 2 minute person go back with the flashlight. You have used 4 minutes.

    Now have the 5 minute and 10 minutes person cross with the flashlight. You have used 14 minutes.

    Now have the 1 minute person go back with the flashlight. You have used 15 minutes.

    Now have the 1 minute person and 2 minute person cross with the flashlight. You have used 17 minutes and everyone is across.

    ReplyDelete
  2. ChuckFebruary 25, 2007 at 10:18 AM

    First have the 1 minute and 2 minute person cross together with the flashlight. You have used 2 minutes.

    Now have the 2 minute person go back with the flashlight. You have used 4 minutes.

    Now have the 5 minute and 10 minutes person cross with the flashlight. You have used 14 minutes.

    Now have the 1 minute person go back with the flashlight. You have used 15 minutes.

    Now have the 1 minute person and 2 minute person cross with the flashlight. You have used 17 minutes and everyone is across.

    ReplyDelete
  3. AnonymousFebruary 25, 2007 at 10:30 AM

    first 2nd guy and 1st guy goes

    total time---2 mins

    then 2nd guy comes back

    total time 2+2=4 mins

    then 3rd and the last guy go
    total time=4+10=14mins

    then 1st guy comes back
    total time=14+1=15 mins


    then 1st and 2nd guy go

    totl time now=15+2=17 mins

    ReplyDelete
  4. AnonymousJuly 15, 2010 at 10:15 AM

    (or)
    1min and 2 min guys cross the bridge
    2 mins used
    1 min guy comes back
    2 more mins used
    so 2+1 = 3 so far
    now 5 and 10 min guys cross the bridge
    10 mins used
    In total 10+3 = 13 mins used
    now 2 mins guy comes back
    so 13+2 =15 used
    and now 1min and 2 min guys go back in 2 mins
    so15+2 = 17 mins

    ReplyDelete

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