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Ruler Puzzle
Posted: Fri Jan 15, 2010 6:38 pm
by Eoin Monaghan
A ruler company called StraightLine has been making rulers which are 13cm long. But the company is poor and can only afford to put enough ink on for FOUR digits. The manager is smart and realises he can use 4 numbers but still be able to measure 1cm to 13cm. What 4 measurements does he make?
Example. The numbers 1cm, 4cm, 8cm and 13cm.
You could make 1cm because it is there, 2cm you can't, 3cm by going from 1cm to 4cm, 4cm is there, 5cm by going from 8cm to 13cm and so on and so forth. I got this as a puzzle in school once.
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:05 pm
by Eoin Monaghan
Kieran has PMed me a correct answer (different to mine, but still valid).
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:15 pm
by Gavin Chipper
1, 4, 5, 11
1=1
13-11=2 (measuring backwards from the end)
4-1=3
4=4
5=5
11-5=6
11-4=7
13-5=8
13-4=9
11-1=10
11=11
13=1=12
Whole ruler=13
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:16 pm
by Kirk Bevins
Eoin Monaghan wrote: But the company is poor and can only afford to put enough ink on for FOUR measurements.
Would be fine if you said 4 digits, but 4 measurements? Surely the company can afford maybe 6 or 7 digits? Nice puzzle but a bit contrived.
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:20 pm
by Eoin Monaghan
Gavin is correct, again with a different answer to mine.
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:23 pm
by Matt Morrison
Gavin wins. Kieran's just fucking spooky these days, reading the forum without signing in, bad jokes in aptochat, PMing puzzle answers when everyone else is taking part in the thread. The new Bolas.
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:29 pm
by Michael Wallace
Kirk Bevins wrote:Nice puzzle but a bit contrived.
How were you ever a maths teacher?
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:33 pm
by Eoin Monaghan
Howard has it right with another different answer, clearly more than one method of solving.
Additional puzzle: How many different methods can you find?
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 7:34 pm
by Jimmy Gough
Matt Morrison wrote:Kieran's just fucking spooky
Yep.
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 8:15 pm
by Howard Somerset
Eoin Monaghan wrote:Additional puzzle: How many different methods can you find?
I've found
three essentially different ways
but that's actually six if you include reflections.
1, 2, 6, 10
1, 4, 5, 11
1, 6, 9, 11
and their reflections
2, 8, 9, 12
2, 4, 7, 12
3, 7, 11, 12
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 8:50 pm
by Ian Volante
Howard Somerset wrote:Eoin Monaghan wrote:Additional puzzle: How many different methods can you find?
I've found
three essentially different ways
but that's actually six if you include reflections.
1, 2, 6, 10
1, 4, 5, 11
1, 6, 9, 11
and their reflections
2, 8, 9, 12
2, 4, 7, 12
3, 7, 11, 12
They all have more than four digits!
Re: Ruler Puzzle
Posted: Fri Jan 15, 2010 9:13 pm
by Howard Somerset
Ian Volante wrote:They all have more than four digits!
lol
As has the original example in the question Eoin posed. I think the original post should have said NUMBERS rather than DIGITS.