Chapter 7 - Exponents and Exponential Functions - 7-3 Multipying Powers with the Same Base - Practice and Problem-Solving Exercises - Page 430: 55

$8 \times 10^{-8}$

$a^m \cdot a^n = a^{m+n}$ Multiply the corresponding parts and use the rule above when necessary to obtain: $=(0.2\cdot 4) \times (10^{5} \cdot 10^{-12}) \\=0.8 \times 10^{5+(-12)} \\=0.8 \times 10^{-7} \\=8(10^{-1}) \times 10^{-7} \\=8 \times 10^{-1+(-7)} \\=8 \times 10^{-8}$