I have 25 coins each weighing 1tr.oz in a closed cylindrical tube weighing 6.5g. The tube is 10.6cm long and has a diameter of .8in. What is the SI-unit density of the tube, disregarding any air inside it?
1 troy ounce = 31.1 g
Total mass = 25 coins * 31.1 g/coin + 6.5 g = 784.0 g

1 inch = 2.54 cm
Volume = L * pi * r^2 = 10.6 cm * 3.14 * (0.8 in * 2.54 cm/in)^2 = 33.28 cm * (2.03 cm)^2 = 137.4 cm^3

Density = mass/volume = (784.0 g) / (137.4 cm^3) = 5.71 g/cm^3
Based on coin density, what material are these coins made of?
The density of just the coins (disregarding the tube) is about 5.659 g/cm^3. Tin has a density of approximately 5.765 g/cm^3, making it a likely metal for the coins to be made of.