lateral thinking puzzle

Four friends need to cross a dangerous 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?

#Puzzle #Genius

Easy Math Editor

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`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$

Comments

answer 21 minutes

Raghunathan N. - 6 years, 7 months ago

answer 17 minutes

**Left side**        || **on boat**       ||     **Right Side
1) 1,2,7,10          ||                   ||No one  ( starting stage)
2) 7,10              || 1,2   cross river ||  1,2   and time =2 min
3) 1,7,10            || 1 return with boat||  2        and time =1 min
4) 1                 || 7,10 cross river  || 2,7,10 and time =10 min
5) 1,2               || 2 return with boat|| 7,10 and time =2 min
6)  No one           || 1,2 cross river   || 1,2,7,10 and time =2 min

So the total time =17 min

Krishana Kant Pareek - 6 years, 2 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$