To do a quotient between two numbers in scientific notation we must do the usual division with the number, and subtract the exponents, for example:
[tex]9\times10^7\div3\times10^3=3\times10^4[/tex]Therefore, we must divide
[tex]7.2\times10^3\div5\times10^5[/tex]Do the division:
[tex]\frac{7.2}{5}=1.44[/tex]Now we do the division of the exponents
[tex]\frac{10^3}{10^5}=10^{3-5}=10^{-2}[/tex]Now we put it all together:
[tex]7.2\times10^3\div5\times10^5=1.44\times10^{-2}[/tex]