The total weight of 20 bars of copper is 20*90 = <<20*90=1800>>1800kgs
If a copper bar weighs 90 kgs, and a steel bar weighs 20 kgs more than a copper bar, the weight of a steel bar is 90+20 = <<90+20=110>>110 kgs.
If a bar of steel weighs 110 kgs, 20 bars will weigh 20*110 = 2200kgs
The total weight of 20 bars of copper and steel is 2200+1800 = <<2200+1800=4000>>4000 kgs
A bar of steel weighs twice the mass of a bar of tin, meaning a bar of tin weighs 110/2 = <<55=55>>55 kgs
The total weight of 20 bars of tins is 55*20= <<55*20=1100>>1100 kgs
The total weight of 20 bars of each metal is 4000+1100 = 5100 kgs
#### 5100