A problem by Chinmay Shah

Level pending

A good puzzle....crack it...

Four friends A, B, C, D Need to cross the bridge.. They start on the same time to cross the bridge. A maximum of 2 peoples can cross at a time.. It is night and they have just 1 lamp. People that cross the bridge must carry the lamp to see the way.. A pair must walk together at the speed of slower person... Speeds of A: 1 minute to cross bridge B: 2 minutes to cross bridge C: 7 minutes to cross bridge D: 10 minutes to cross bridge

Now question is... "what is the total minimum time required by all 4 friends to cross the bridge....? Scratch ur brains...

The answer is 17.

2 solutions

Vaibhav Nayak
Feb 18, 2014

The answer is 17 , not 21 .

$A$ and $B$ go, $A$ comes back. Time required: $2+1=3$

$C$ and $D$ go, $B$ comes back. Time required: $10+2=12$

$A$ and $B$ go. Time required: $2$

Total time(min) : $3+12+2=\boxed{17}$

yeah i think its 17

send the two fastest

send back the slowest of the two with lamp

send the two slowest

send back the fastest

repeat till all have reached the destination

Rajeev Sebastian - 6 years, 10 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

A problem by Chinmay Shah

The answer is 17.

2 solutions

0 pending reports