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# 4 man crossing a bridge puzzle

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• 1 and 2 go across 2 min, 1 comes back 3 min, 5 and 10 cross 13 min, 2 goes back 15 min, 1 and 2 cross 17 min.

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### 4 man crossing a bridge puzzle

1. 1. Four Men Crossing a Bridge
2. 2. Four Men Crossing a Bridge <ul><ul><li>There are four men who would all like to cross a rickety old bridge. (Perhaps it is more accurate to say that they'd like to get to the other side). </li></ul></ul>
3. 3. Four Men Crossing a Bridge <ul><ul><li>The old bridge will only support 2 men at a time, and it is night time, so every crossing must use the one flashlight that they all share. </li></ul></ul>
4. 4. Four Men Crossing a Bridge <ul><ul><li>The four men each have different walking speeds; the fastest each of them can cross is </li></ul></ul><ul><ul><ul><li>1 minute, </li></ul></ul></ul><ul><ul><ul><li>2 minutes, </li></ul></ul></ul><ul><ul><ul><li>5, minutes, and </li></ul></ul></ul><ul><ul><ul><li>10 minutes. </li></ul></ul></ul>
5. 5. Four Men Crossing a Bridge <ul><ul><li>If they pair up, since they must share the flashlight, they can only cross in the time that it would take the slower of the two. </li></ul></ul>
6. 6. Four Men Crossing a Bridge <ul><ul><li>Given that the shortest time to get them all across is 17 minutes total, how should they all cross? </li></ul></ul>
7. 7. Four Men Crossing a Bridge