# How do you simplify 4.7-1.9?

Dec 11, 2016

The explanation takes longer than doing the actual mathematics.

$2.8$

#### Explanation:

$\textcolor{b l u e}{\text{Ideally this is what the calculation should look like}}$

$\textcolor{b r o w n}{\text{Each person has to find the way that works best for them}}$

A portion of this calculation is done in my mind

$4.7$
$\underline{1.9} \leftarrow \text{ subtract}$
$2.8$

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$\textcolor{b l u e}{\text{Explaining my thought process}}$

$\textcolor{b l u e}{\text{Step 1}}$
Take 1 from the 4 and put it with the 0.7
But $1 = \frac{10}{10} \text{ and "0.7=7/10" so we end up with } \frac{17}{10}$

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

It looks like this:$\text{ "4.7" "->" } {\cancel{4}}^{3} . {\cancel{7}}^{17}$
............................................................................................
$\textcolor{b l u e}{\text{Step 2}}$

Putting it all together:

$4.7 \text{ } {\cancel{4}}^{3} . {\cancel{7}}^{17}$
$\underline{1.9} \leftarrow \text{ subtract "ul(1color(white)(.).color(white)(.)9) larr" subtract}$
$\text{ } 2 \textcolor{w h i t e}{.} . \textcolor{w h i t e}{.} 8$

Dec 11, 2016

$\textcolor{b l u e}{\text{A shortcut thinking process}}$
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 $\to 2.7 + 0.1 = 2.8$