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1.       On average, the moon takes 27 days, 7 hours, and 43.2 minutes to make a complete circuit around the Earth. Express this time in hours.

 \(27days\ \frac{24hr}{day}=648\ hr\)
\(43.2\ \min\ \frac{hr}{60\ \min}=0.720\ hr\)
\(648\ hr\ +0.720\ hr\ +7\ =655.720\)
We can question our precision for the value of 43.2 minutes.  The other values are more or less exact. Following the rule of addition we then end up with 6 significant figures.