if you solve this youre really a genius..:)

Computer Science Level 2

Four people need to cross a rickety bridge at night. Unfortunately, they have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge. Times for each person: 1 min, 2 mins, 7 mins and 10 mins. What is the shortest time needed for all four of them to cross the bridge?


The answer is 17.

Aman Khalfay by Aman Khalfay , 22, India

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2 solutions

  1. Person 1 min and 2 mins cross the bridge. Need 2 mins
  2. Person 1 min back. Need 1 min
  3. Person 7 mins and 10 mins cross the bridge. Need 10 mins
  4. Person 2 mins back. Need 2 mins
  5. Person 2 mins and 1 min cross the bridge. Need 2 mins.
    Total time = 2+1+10+2+2 = 17. We put person 7 mins and 10 mins to cross together so not too wasting time. And using person 1 min and 2 mins for pick other persons since they cost less time
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This question is in the Ted-Ed riddle series.

Daniel Xian - 2 years, 4 months ago
Saya Suka
Apr 26, 2021

Answer
= ceiling[1,2] + 1 + ceiling[10,7] + 2 + ceiling[1,2]
= 2 + 1 + 10 + 2 + 2
= 17 minutes


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