### Letter

With letters you may calculate just as with numerals. Even a child understands that

1

a+ 1a= 2a

But there is of course more behind it.

##### Explanation

Often you work with letters because you do not know the exact value. You call such numbers *x, y, z *or *p, q, r*. For historical reasons, we use small letters. Usually, you have a combination of letters and numerals. That you see at

It consists of the numerals 1, 2 and 5 and the letters *a* en *b*. The digits form the decimal number 125, where the 1 represents 100, the 2 is for 20 and the 5 is for 5. The letters make the product *a × b*. If you write with brackets you get

A trickier number is

Here are the digits pulled apart, because it is easier to read. A different matter is

what you can better write as

Work as clear as possible.

##### Additional information

The French mathematician François Viète (1540 - 1603) introduced calculations with letters.