A high voltage wire for transmission of electricity across the country is made of 10 aluminium wires (resistivity of 2.5 × 10-8 m) wound together with 15 copper wires (resistivity of 1.5 x 10-8 m). If all of the wires have a radius of 2.0 mm, calculate the overall resistance of 20 km of cable to two significant figures. (The aluminium is there to give strength to the cable.)
