Question

How do you simplify `4.7-1.9`?

Answer 1

The explanation takes longer than doing the actual mathematics.

`2.8`

Explanation:

`color(blue)("Ideally this is what the calculation should look like")`

`color(brown)("Each person has to find the way that works best for them")`

A portion of this calculation is done in my mind

`4.7`
`ul(1.9) larr" subtract"`
`2.8`

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
`color(blue)("Explaining my thought process")`

`color(blue)("Step 1")`
Take 1 from the 4 and put it with the 0.7
But `1=10/10" and "0.7=7/10" so we end up with "17/10`

Because we have removed 1 from the 4 it becomes 3.

It looks like this:`" "4.7" "->" "cancel(4)^3 . cancel(7)^17`
............................................................................................
`color(blue)("Step 2")`

Putting it all together:

`4.7" "cancel(4)^3 . cancel(7)^17`
`ul(1.9) larr" subtract "ul(1color(white)(.).color(white)(.)9) larr" subtract"`
`" "2color(white)(.). color(white)(.)8`

Answer 2

`color(blue)("A shortcut thinking process")`
2.8

Explanation:

think of 1.9 as `2-0.1`

So if you subtract 2 you have removed 0.1 too much. So you put it back.

`4.7-2 = 2.7`

Now put back the 0.1 `->2.7+0.1=2.8`