## Archive for the ‘Simple’ Category

### Efficient Casting of Roman Numerals for Clocks

Sunday, 25 March 2012

Using IIII rather than IV, the symbols on a 12-hour clock face with roman numerals number:

twenty Is
four Vs
four Xs

so a single mould

VIIIIIX

can be cast four times, with each casting cut twice, in order to make the correct number of numerals:

VIII — I — IX
VI — II — IIX
VII — III — X
V — IIII — IX

The IIX and one of the IXs are turned to form XII and XI.
(more…)

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### English Letter Names

Saturday, 12 February 2011

Table…

### Learning the Multiplication Tables

Tuesday, 21 December 2010

In a previous post, I tried to show that learning the multiplication tables need not be daunting for children (or even adults). Here are a few odd methods and techniques that might also help.

### Adding Percentages (%)

Thursday, 15 October 2009

A percentage (%) is just a ratio, parts per 100.

You can multiply by a percentage to get a proportion of the total:

P% of T = T × P / 100

A percentage has no ‘dimension’, or units. It is a ‘pure number’. It can’t really be added or a quantity (other than to another pure number). To add a percentage really means to add a proportion of the original amount:

“A + P%” = A × (1 + P / 100)

### Colour Mixing

Sunday, 26 April 2009

There seems to be some confusion about what the primary and secondary colours are. Well, it depends.

### Planetary Mnemonic

Tuesday, 21 April 2009

Here’s something I noticed that might help people to remember the order of some of the planets – mainly the gas giants.

Beyond Mars are:

• Jupiter
• Saturn
• Uranus
• Neptune

notice the initial letters in the order SUN away from the Sun.

### Multiplication Tables

Wednesday, 8 April 2009

When I was at school, we were taught the multiplication tables to 12. Perhaps this limit was a hangover from Imperial measurement and old money. Now children are taught to 10.

1 2 3 4 5 6 7 8 9 10 11 12
2 4 6 8 10 12 14 16 18 20 22 24
3 6 9 12 15 18 21 24 27 30 33 36
4 8 12 16 20 24 28 32 36 40 44 48
5 10 15 20 25 30 35 40 45 50 55 60
6 12 18 24 30 36 42 48 54 60 66 72
7 14 21 28 35 42 49 56 63 70 77 84
8 16 24 32 40 48 56 64 72 80 88 96
9 18 27 36 45 54 63 72 81 90 99 108
10 20 30 40 50 60 70 80 90 100 110 120
11 22 33 44 55 66 77 88 99 110 121 132
12 24 36 48 60 72 84 96 108 120 132 144

Given that the 1 and 10 times tables are obvious, and that multipliacation of numbers is commutative (so that six eights equals eight sixes), there are only really 36 facts to learn (shown in  blue ).

Once the relatively easy 2-, 3-, 4- and 5-times tables have been learnt, only 10 number facts remain:

1 2 3 4 5 6 7 8 9 10
2 4 6 8 10 12 14 16 18 20
3 6 9 12 15 18 21 24 27 30
4 8 12 16 20 24 28 32 36 40
5 10 15 20 25 30 35 40 45 50
6 12 18 24 30 36 42 48 54 60
7 14 21 28 35 42 49 56 63 70
8 16 24 32 40 48 56 64 72 80
9 18 27 36 45 54 63 72 81 90
10 20 30 40 50 60 70 80 90 100

Hopefully, this will make learning your tables seem a little less daunting.

### Bugzilla Links

Wednesday, 8 April 2009

When you type a comment or a description (which is “comment 0”) for a bug in Bugzilla, certain phrases are treated as special.

For example, the word “bug” followed by a space and then a decimal number is converted into a link to another bug. Therefore, rather than saying

`See also bugs 1234 and 2345.`

you could instead say

`See also bug 1234 and bug 2345.`

and the links will be formed by “autolinkification”—you will only see the links after you click the [commit] button.

For more information, see the Bugzilla help topic.

### Possessive Apostrophes

Tuesday, 7 April 2009

There’s a very easy rule for using apostrophes to indicate possession.