A little logic game

[tuscan_v8]

A = 10 mins
B = 5 mins
C = 2 mins
D = 1 min

We need to cross the bridge, the problem is only 2 persons can cross at a time and one have to go back.

Your task is to take A B C D to other side of the bridge (to attend a concert) in minimum time.

What is the best time you can achieve (the best is 17 mins) tell me how you did it?

I've only managed 19 mins

A+D = 10
<- D = 1
B+D = 5
<- D = 1
C+D = 5
Total = 19 mins

[jimothy]

tuscan_v8 said:

A = 10 mins B = 5 mins C = 2 mins D = 1 min We need to cross the bridge, the problem is only 2 persons can cross at a time and one have to go back. Your task is to take A B C D to other side of the bridge (to attend a concert) in minimum time. What is the best time you can achieve (the best is 17 mins) tell me how you did it? I've only managed 19 mins A+D = 10 <- D = 1 B+D = 5 <- D = 1 C+D = 5 Total = 19 mins

C+D = 2
<- C = 2
A+B = 10
<- D = 1
C+D = 2
Total = 17 minutes

[tuscan_v8]

That was quick !! know anymore?

[nel]

tuscan_v8 said:

I've only managed 19 mins A+D = 10 <- D = 1 B+D = 5 <- D = 1 C+D = 5 Total = 19 mins

Total = 22 minutes shirley!

Not surprising that you couldn't do it if you can't add up!

[omitchell]

jimothy said:

tuscan_v8 said: A = 10 mins B = 5 mins C = 2 mins D = 1 min C+D = 2 <- C = 2 A+B = 10 <- D = 1 C+D = 2 Total = 17 minutes

surely c+d = 3 not 2 minutes and a+b = 15 minutes giving you a time of 24 mins? or have i got it completely wrong

[Carrera2]

This is an advanced version of the hen/seed/fox problem.

Bear that in mind when trying to solve it.

[Einion Yrth]

omitchell said:

jimothy said: tuscan_v8 said: A = 10 mins B = 5 mins C = 2 mins D = 1 min C+D = 2 <- C = 2 A+B = 10 <- D = 1 C+D = 2 Total = 17 minutes surely c+d = 3 not 2 minutes and a+b = 15 minutes giving you a time of 24 mins? or have i got it completely wrong

any pairing takes the longest time of the two, not the sum of the times.

[omitchell]

oh, ok thanks for the clarification

[zippee]

omitchell said:

jimothy said: tuscan_v8 said: A = 10 mins B = 5 mins C = 2 mins D = 1 min C+D = 2 <- C = 2 A+B = 10 <- D = 1 C+D = 2 Total = 17 minutes surely c+d = 3 not 2 minutes and a+b = 15 minutes giving you a time of 24 mins? or have i got it completely wrong

But if c+d are walking across together then it'll be the time taken for both to get across, hence they both do it in 2 minutes. Would be 3 minutes if they were crossing seperately.

[wedg1e]

How about if, say, A + B walk across. B gets there in 5 and while A is still on the bridge C sets off. C will overtake A and when C arrives, B sets off back (so still two crossing!) and so on...