Brain Teasers

[crimson_b1ade]

AE> 10 (10)

<A p 1 (11)<>AD> 5 (16)

<A p 1 (17)<>AC> 3 (20)

AB> 2 (23)

"A" goes back to get everyone else since he's the fastest.

23 minutes. does this work?

5 men of equal weight need to cross a bridge in the fastest time possible.

The bridge is not very sturdy so only 2 men can cross the bridge at the same time.

The men only have 1 torch. It is very dark so the bridge can only be traversed if someone is carrying the torch. The men crossing the bridge must carry the torch (the way cannot be shone by someone holding the torch from either end) and they must stay together during the crossing.

This means that once 2 men have crossed the bridge, the torch has to be taken carried back to the other side to the remaining men otherwise they would not be able to cross. The torch cannot be thrown back (or some other workaround): it must be carried back.

The men have different fitness levels which means that it takes them different amounts of time to cross the bridge:

Man A       1 minute
Man B       2 minutes
Man C       3 minutes
Man D       5 minutes
Man E       10 minutes

So, for example, if Man A and Man E cross the bridge together it would take them 10 minutes because they must stay together.


There are no tricks in this question. They all must cross the bridge (no swimming etc...); it is a straightforward maths problem: what is the quickest way for them to cross the bridge?

 

[Colin Legg]

AE> 10 (10)

<A (11)< 1 p>AD> 5 (16)

AC> 3 (20)

AB> 2 (23)

"A" goes back to get everyone else since he's the fastest.

23 minutes. does this work?

That's the right sort of idea and it's a good, logical approach.
However, it is possible to do it in less than 23 minutes.

 

[Sandeep Warrier]

A & B go first => 2 min
B comes back => 2 min
D & E go => 10 min
A comes back => 1 min
A & C go => 3 min
A comes bacl => 1 min
A & B go => 2 min

Total time taken - 2+2+10+1+3+1+2 => 21 min
<input id="gwProxy" type="hidden"><!--Session data--><input *******="jsCall();" id="jsProxy" type="hidden">

 

[Colin Legg]

A & B go first => 2 min
B comes back => 2 min
D & E go => 10 min
A comes back => 1 min
A & C go => 3 min
A comes bacl => 1 min
A & B go => 2 min

Total time taken - 2+2+10+1+3+1+2 => 21 min

That's correct!

 

[Sandeep Warrier]

That's correct!

I solved a similar puzzle consisting of 4 members a couple of years back... it came in as a flash file complete with 2 kids, a dad and a grumpy old grandpa and a wobbling bridge ...

Good to know I still remembered the logic....
<input id="gwProxy" type="hidden"><!--Session data--><input *******="jsCall();" id="jsProxy" type="hidden">

 

[litrelord]

AE> 10 (10)

<A p 1 (11)<>AD> 5 (16)

<A p 1 (17)<>AC> 3 (20)

AB> 2 (23)

"A" goes back to get everyone else since he's the fastest.

23 minutes. does this work?

This was what I got only you dont' need to add on 1 minute each time for A to get across as he's goign at the same time. This gives 20 mins...

AB 2 Mins
AC +3 Mins (5 Mins)
AD +5 Mins (10 Mins)
AE +10 Mins (20 Mins)

Unless I'm doing something wrong.

Now is anyone going to post the answer to the 5x5 grid with 5 dogs and 3 cats because I just can't work it out and it's making me feel stupid

Nick

 

[Colin Legg]

This was what I got only you dont' need to add on 1 minute each time for A to get across as he's goign at the same time.

In that solution, each time man A walks over with someone, he has to walk back across the bridge again with the torch to take the next man across. That's where the extra 1 minute on each "crossing" is coming from.

21 minutes is the fastest.

 

[litrelord]

See, it's no wonder I can't work out the dogs and cats one if I overlook such a simple thing as the return journey.

Must be time for more (or maybe less) coffee!

Nick

 

[pgc01]

Hi all

Another brain teaser.

In a chess board you remove 2 squares at opposite corners (ex. A1 and H8). Is it possible to enter by one of these corners with a rook and leave by the other corner after passing by all the squares in the board?

Remember that a rook only moves either horizontally or vertically.

 

[Sandeep Warrier]

Hi Pedro,

Good question!!!

Tried out some basic combos.... always one square left out....

Excel Workbook
	A	B	C	D	E	F	G	H
1	Start	3	4	5	6	7	8	9
2	1	2	15	14	13	12	11	10
3	18	17	16	23	24	25	26	27
4	19	20	21	22	31	30	29	28
5	36	35	34	33	32	43	44	45
6	37	38	39	40	41	42	47	46
7	54	53	52	51	50	49	48	Left Out
8	55	56	57	58	59	60	61	End
Sheet1

Excel 2003



Need to get in more thinking done i guess