# Blank ruler riddle

#### Greg Bernhardt

With a blank ruler (without marks) of exactly 36 cm you can only measure 36 cm. Now you are allowed to set 8 marks so that you can read off all full centimeter values from 1 to 36 cm directly from the ruler.

Where must these 8 marks be?

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#### Mentat

At the beginning, and a centimeter apart each, is my guess.

#### Greg Bernhardt

Originally posted by Mentat
At the beginning, and a centimeter apart each, is my guess.
You can only have eight marks

#### iansmith

Staff Emeritus
Gold Member
You place the firts mark at 4 cm and then following 4 cm after. Therefore, you have a mark at 4, 8, 12, 16, 20, 24, 28, 32.

#### Astrophysics

0,5 cm
1,0 cm
3,0 cm
6,0 cm
10,0 cm
15,0 cm
21,0 cm
28,0 cm

just guessing [?]

No idea. Every 4.5 centimeters?

Also to point out about the last brain teaser, I would have said compressed gasses (as it seems recent planetary science has led to the idea that outter planets would not have enough rocky material that far out to form large rocky cores. Mainly from evidence from exosolar systems, but ultimately I suppose it is the accepted answer).

#### Greg Bernhardt

Originally posted by iansmith
You place the firts mark at 4 cm and then following 4 cm after. Therefore, you have a mark at 4, 8, 12, 16, 20, 24, 28, 32.
How do you measure 3cm or 5cm then?

#### Astrophysics

maybe it's time for another wild guess, how about:

1,0 cm
2,0 cm
3,0 cm
4,0 cm
5,0 cm
6,0 cm
7,0 cm
8,0 cm

together they add up to 36 cm

#### cytokinesis

First at 18 in the middle
Then at 9
At 4.5
Divide that space in 3 so you have 1.5 and 3.0
And divide the 3.0 marking into 3 as well.

#### cytokinesis

*after you have the first centimetre then you can copy the 1 cm length over the ruler to measure everything

#### Greg Bernhardt

Originally posted by cytokinesis
First at 18 in the middle
Then at 9
At 4.5
Divide that space in 3 so you have 1.5 and 3.0
And divide the 3.0 marking into 3 as well.
all full centimeter values from 1 to 36 cm directly from the ruler. how do you find 5cm?
after you have the first centimetre then you can copy the 1 cm length over the ruler to measure everything
Nah, thats cheating, you must be able to read all full centimeter values from 1 to 36 cm directly from the ruler. no copying or using the ruler twice.

#### Hurkyl

Staff Emeritus
Gold Member
I will mark
1, 3, 6, 13, 20, 27, 31, and 35 centimeters on my ruler.

#### Greg Bernhardt

Originally posted by Hurkyl
I will mark
1, 3, 6, 13, 20, 27, 31, and 35 centimeters on my ruler.
Hurkyl wins the point! btw Hurkyl check your pm

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