I also had this question on my math test the other day and really didn't understand how to do it. I would love to understand how to solve such a problem in the future.
The question is: The gold pavilion in the city of Kyoto is covered with gold leaf. Gold leaf has a thickness of 100 nm (nanometres) and is made from gold bars. A gold bar has a volume of 0.65 dm^3. How many square metres can the gold leaf from a gold bar cover?
I thought I would try to convert the nanometres into decimetres and then calculate the volume. In the end it didn't work so I turn here. How do I do it?
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I believe you just have to equate the volume of the gold bar to the volume of the gold leaf. If area covered is $A$ $m^2$, then we have: $$0.65×10^{-3}=100×10^{-9}A$$ Hence you get your answer.