解：
(1)一張復(fù)印紙的厚度?$d=\frac{h}{n}=\frac{5cm}{500}=0.01cm = 1×10^{-4}m。$?
(2)一包復(fù)印紙的質(zhì)量?$m = 70g/m^{2}×500×A4紙面積，$?A4紙尺寸約為?$0.21m×0.297m，$?則?$A4$?紙面積?$S = 0.21m×0.297m\approx0.0624m^{2}，$?
所以?$m = 70g/m^{2}×500×0.0624m^{2}=2184g = 2.184kg。$?
一包復(fù)印紙的體積?$V = S_{總}(cāng)h=0.0624m^{2}×0.05m = 3.12×10^{-3}m^{3}。$?
該復(fù)印紙的密度?$\rho=\frac{m}{V}=\frac{2.184kg}{3.12×10^{-3}m^{3}} = 0.7×10^{3}kg/m^{3}。$?
答：
(1)一張復(fù)印紙的厚度為?$1×10^{-4}m；$?
(2)該復(fù)印紙的密度為?$0.7×10^{3}kg/m^{3}。$?
