Answer
a) $680000$
b) $60000$
Work Step by Step
a) $(2\cdot10^9)(3.4\cdot10^{-4})=2\cdot3.4\cdot10^{9-4}=6.8\cdot10^5=680000$
b) $(1.2\cdot10^7)(5\cdot10^{-3})=1.2\cdot5\cdot10^{7-3}=6\cdot10^4=60000$
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