## Monthly Archives: June 2010

## Mickey Mouse the drug addict

## IPv6 subnet cheat sheet

Since it was very hard indeed to find a cheat sheet like this online for IPv6 subnetting or CIDR notation, I’m putting it out there:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 |
2001:0DB8:0400:000e:0000:0000:0000:402b XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX:XXXX ||| |||| |||| |||| |||| |||| |||| ||| |||| |||| |||| |||| |||| |||128 ||| |||| |||| |||| |||| |||| ||124 ||| |||| |||| |||| |||| |||| |120 ||| |||| |||| |||| |||| |||| 116 ||| |||| |||| |||| |||| |||112 ||| |||| |||| |||| |||| ||108 ||| |||| |||| |||| |||| |104 ||| |||| |||| |||| |||| 100 ||| |||| |||| |||| |||96 ||| |||| |||| |||| ||92 ||| |||| |||| |||| |88 ||| |||| |||| |||| 84 ||| |||| |||| |||80 ||| |||| |||| ||76 ||| |||| |||| |72 ||| |||| |||| 68 ||| |||| |||64 ||| |||| ||60 ||| |||| |56 ||| |||| 52 ||| |||48 ||| ||44 ||| |40 ||| 36 ||32 |28 24 |

## WTF animal gallery

## Coolest tattoo I’ve seen

## Phonebook carvings

## Dinosaurs were warm blooded

A nice article detailing how sea dwelling dinosaurs like ichthyosaurus, plesiosaurus and mosasaurus were most likely warm blooded.

## Wasps that genetically engineer oak trees

This video, narrated by Attenborough, shows how wasps can modify oak trees to their advantage. Fascinating stuff…

## The surface area required to power the earth

## Multiplication of roman numerals

I came across this awesome article explaining how romans multiplied their numerals, which I’ve always wondered about. Follow the link to the full article for the explanation on why this actually works.

It is often said that an important advantage of the decimal notation over the Roman one is that makes multiplication of numbers much easier. Adding CLXXVII to XXIII may be relatively straightforward–but how about multiplying the two?

You can verify that indeed 177 x 23 = 4071. The Romans did all this using their own cumbersome notation, but people used to handling numbers were experienced in doubling and halving, and could carry it out fairly quickly. Doubling can be relatively simple: XXIII doubled is XXXXVI, doubled again DXXXXII (Romans wrote 4=IIII,40=XXXX, and notations like 4=IV were only introduced in the middle ages). Like the method we use, it reduced the multiplication of two numbers to addition, which Roman numerals could handle.

It is indeed easier to multiply these as decimal numbers 177 by 23, but the Romans also had a multiplication method of their own. It was probably discovered by trial and error, and it always worked, though the Romans did not know why.

Here the method is described, and its secret explained. The Romans started by writing the numbers next to each other. Of course, they used Roman numerals–but to make it clear in what follows,

heredecimal notation will be used throughout. Suppose we need to derive177 x 23

After writing down the numbers (here the multiplication sign was added),

halvethe first one anddoublethe second, writing the new numbers below the preceding ones. If the number being halved is odd, just ignore the remainder. Repeat this operation as long as you can:

177 x 23 88 46 44 92 22 184 11 368 5 736 2 1472 1 2944 Now

cross outin thesecond columnall numbers where the corresponding number in thefirst columniseven:

177 x 2388 46 44 92 22 184 11 3685 7362 1472 1 2944Then add up the remaining numbers:

23 + 368 + 736 + 2944 = 4071