The first thing we need to do is sum the weight of the materials in the bridge, so we have that
[tex]1000\text{ tons + 400 tons + 200 tons = 1600 tons}[/tex]Now we have that the weight of glass and granite in the bridge is 200 tons, so the fraction is
[tex]\frac{200}{1600}=\text{ }\frac{2}{16}=\frac{1}{8}[/tex]So the answer is 1/8.
