In this video (at around 1:20) Sal does the following: $$40 + \frac{9}{10} \cdot 40 = 40(1 + \frac{9}{10}) = 40 \cdot 1.9$$
I can't figure out that first part where he goes from $$40 + \frac{9}{10} \cdot 40$$ to $$40(1 + \frac{9}{10})$$
I thought he was factoring out a $40$ from $40 + \frac{9}{10}$ but to my knowledge he's supposed to divide both numbers on either side of the $+$ sign if he was factoring, is that not so? Which would make it:
$$40(1+\frac{\frac{9}{10}}{40})$$
What am I missing here? Is he even factoring or is it something else entirely?
Note that$$40\left(1+\frac9{10}\right)=40\times1+40\times\frac9{10}=40+\frac9{10}\cdot40.$$