The scientific notation:
[tex]a\cdot10^k,\ 1\leq a < 10,\ k\in\mathbb{Z}[/tex]
[tex](3\cdot10^2)(5\cdot10^5)=[(3)(5)][(10^2)(10^5)]=15\cdot10^{2+5}=15\cdot10^7\\\\=1.5\cdot10\cdot10^7=1.5\cdot10^8\\\\Answer:\ (3\cdot10^2)(5\cdot10^5)=1.5\cdot10^8\\\\Used\ a^n\cdot a^m=a^{n+m}[/tex]