Four people (1 Viewer)

[Rkiuyto]

Four people, A, B, C, and D, are on one side of a bridge, and they all want to cross the bridge. However, it's late at night, so you can't cross without a flashlight. They only have one flashlight. Also, the bridge is only strong enough to support the weight of two people at once. The four people all walk at different speeds: A takes 1 minute to cross the bridge, B takes 2 minutes, C takes 5 minutes, and D takes 10 minutes. When two people cross together, sharing the flashlight, they walk at the slower person's rate. How quickly can the four cross the bridge?

 

[Timothy.Siu]

19 minutes?

 

[dp624]

AD over = 10
A back = 1
AC over = 5
A back = 1
AB over = 2

That's 19?

 

[Timothy.Siu]

doesn't seem like a 2u questions though.

 

[Rkiuyto]

19 minutes?

no it is not true

 

[annabackwards]

doesn't seem like a 2u questions though.

I've never encountered a 2U question like this, but you never know.

19 minutes?

no it is not true

I got 19 from the question too.

Unless person A (who goes back and forth) can begin walking back while the next person (at the starting point) begins walking towards person A so the time is shortened.

 

[~caramello~]

19 minutes?

no it is not true

I got 19 too.
Same method as dp.
Do you have the answers?

 

[Timothy.Siu]

definitely not 2unit then, seems like some puzzle/trick question

 

[lolokay]

what's the answer if it's not 19?

 

[Rkiuyto]

17 min is rite

 

[Timothy.Siu]

17 min is rite

lol how does that work? working out please.

 

[wixxy2348]

17 would be omitting the time that it takes A to cross back... unless A returns WHILE C and D are still walking (returning simultaneously, as there'd still only be the weight of two people on the bridge).
Though that doesn't work as there is only one flashlight.

A must have some insane night vision if that's how the OP worked it out.

My bets are that he's omitted the return time for A.

 

[~caramello~]

May i ask where you got this question from?

 

[Timothy.Siu]

u can do 12 minutes, just wait till day

 

[dp624]

i wonder if you can throw the torch across

 

[wixxy2348]

What if.. B and C only weigh the weight of half a normal person, so they can travel with A and count as 1?
wait... that doesn't work, it'ad be 16.

Throwing the torch across would work but it'd be 15 wouldn't it?

 

[Nevermore]

answer is 17 min

 

[Timothy.Siu]

answer is 17 min

we heard, but why?

 

[~caramello~]

answer is 17 min

working would be nice..