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# Division

The World’s fastest on a computer writes a bit more than 210 words per minute; more than 210 words during those 60 seconds that one minute lasts.

How many words is that every second? Let’s split the 210 words into 60 bits by using a slash $/$ as ‘split into’:

$$210\,\text{words}\,/\,60\,\mathrm s=3\,\text{words/s}$$

In other words, we have used the slash $/$ to mean ‘per’ or ‘divided by’.1 We can call this operation a division. ‘210 words divided by 60 seconds’ or ‘210 words per 60 seconds’ is ‘3 words per second’. The slash even works in this new combined version of a unit: $\text{words/s}$, meaning ‘words per second’.2

Note that division ( $/$ ) and multiplication ( $\cdot$ ) are each other’s “reverse”. ‘To divide’ splits into smaller portions, whereas ‘to multiply’ collects portions again. The 3 words per second will be 210 words after 60 seconds because 3 times 60 is 210.

To give a better overview, especially when writing longer lines, we could choose to tilt the slash down to a horizontal line and write it like:

$$\frac{210\,\text{words}}{60\,\mathrm s}= 3\,\text{words/s}$$

This writing-style is well-known from for example when we write ‘a half’ as $\frac12$. Let’s call it a fraction and the horizontal line a fraction bar.3

• Let’s call the bottom of a fraction the denominator4 since it names the fraction (it tells us if we are splitting into thirds, fourths or fifths etc.; for instance, $\frac18$ is one eighth and $\frac38$ is three eighths), and
• let’s call the top the numerator,5 since it counts the fractions ($\frac18$ is one eighth and $\frac38$ is three eighths).

References:

1. Average typing speed infographic’ (web page), Free Online Typing Tutor, www.ratatype.com/learn/average-typing-speed (accessed Aug. 5th, 2019)
2. Online Etymology Dictionary’ (dictionary), Douglas Harper, www.etymonline.com