Question

How do you add, subtract, divide, and multiply scientific notation expressions

Answer 1

You can call it pemdas .( peranthasis,expression,multiply,divide,add,subtract

Answer 2

Scientific notation is
n*10^x
where 1≤n<10 and x is a whole power
so remember some simple rules
(ab)(cd)=(a)(b)(c)(d)=(ac)(bd)
$\frac{ab}{cd}=( \frac{a}{c})( \frac{b}{d})$
also properties of exponents
$(x^m)(x^n)=x^{m+n}$
and
$\frac{x^m}{x^n}=x^{m-n}$

why is this important?

because
lets say
8*10^9 times 4*10^2
this means
(8)(10^9)(4)(10^2)=(8*4)(10^9*10^2)=32*10^{9+2}=32*10^11, but wait, it has to be less than 10
32=3.2*10^1
32*10^11=3.2*10^1*10^11=3.2*10^12

for division
$\frac{3*10^8}{2*10^3}=( \frac{3}{2})( \frac{10^8}{10^3})$=1.5*10^5

the only way to add or subtract scientifict notation is when the x on the 10^x are the same
otherwise, yo have to expand the expressions