The ‘rickety bridge’ test is a classic brain teaser that only people with a high IQ are likely to crack in less than 30 seconds – so how long will it take you?
Puzzle enthusiasts have been presented with a challenging brainteaser that only people with a high IQ are expected to solve in under 30 seconds.
Known as the ‘rickety bridge’ challenge, the task requires working out the fastest time for four people to cross using just one torch between them during the night.
Just two individuals can cross simultaneously, each taking different amounts of time, whilst the torch must always be carried as crossing without it would be far too perilous.
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The brainteaser has been released by the Geeks for Geeks organisation, which highlights from the outset that the solution isn’t the one that will likely spring to mind first, with the four people crossing the bridge in: 1min, 2mins, 7mins and 10mins. Consequently, many would suggest 21 minutes if the fastest person travels back and forth with the torch.
However, the puzzle’s creator explained: “The initial solution most people will think of is to use the fastest person as an usher to guide everyone across. But it would take longer as 10 + 1 + 7 + 1 + 2 = 21 mins. But can it be the right answer? No. That would make this question too simple even as a warm-up question.”
Rather, we’re informed that the solution involves having the slowest pair – who require 10mins and 7mins – cross together, with the genuine quickest time being 17mins.
The solution involves sending the quickest person across first alongside the second fastest, then keeping the speediest individual on the far side whilst the other returns with the torch for those requiring 7mins and 10mins to cross. At this juncture, the fastest can then make their way back with the torch.
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Geeks for Geeks elaborates: “Let’s brainstorm a little further. To reduce the amount of time, we should find a way for 10 and 7 to go together as they are the slowest among all these.
“If they cross together, then we need one of them to come back to get the others. That would not be ideal. How do we get around that? Maybe we can have 1 waiting on the other side to bring the torch back. This brings us closer to the solution. So let’s put all this together.”
“Steps: 1 and 2 cross the bridge and move to the other side. Now 2 comes back with the torch from the other side. 7 and 10 crosses the bridge and 2 remain to this side only.
“Now 1 comes back with the torch from the other side. At last, 1 and 2 cross the bridge and we are done. Total time taken = 2 + 2 + 10 + 1 + 2 = 17 mins.”
Did you manage to solve it? Let us know in the comments section down below.
