Question #bc8d3

The shortcut method is based on what follows:

I will highlight in red the bit that the shortcut method uses.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("First principle method")`

Using ratios in fractional format.

Lookin at the units to decide how we write this. We are told
'mass per metre' so this is written as:

`("mass")/("metres")->(Kg)/m -> 15/3.25`

The word 'per' means for each of 1. So 'per metre' is for each of 1 metre

Thus we need to change the `3.25` metres to 1 metre
Note that `3.25xx1/3.25 = 1`

So we multiply top and bottom of `15/3.25` by `1/3.25`

`(color(red)(15xx1/3.25))/(3.25xx1/3.25)" "=(color(red)(15xx1/3.25))/1`
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("Shortcut method")`

To determine the mass for one metre apply `color(red)(15-:3.25)`

Now you see where the shortcut approach comes from

This produces a decimal solution which I am choosing to be rounded, so not precise.

`15-:3.25 = 4.61538..... = 4.6` rounded to 2 decimal places

Or you can write: `15/3.25xx 4/4=60/13` which is an exact value