A factory which uses a large amount of coal is situated between two collieries A and B the former being 10 km and the latter 15 km from the factory. A fl eet of lorries of 10 tonne carrying capacity are used for collection of coal from the pitheads. The lorries give an average speed of 20 km per hour when running and regularly take 10 minutes in the factory premises to unload. At colliery A, loading time averages 20 minutes per load, and at colliery B, 30 minutes per load.

Driver’s wages, licences, insurance, depreciation, garage and similar charges are noticed to cost Rs. 10 per hour operated.

Fuel, oil, tyres, repairs and similar charges are noticed to cost Rs. 1 per km run.

Draw up a statement showing the cost per tonne-km of carrying coal from each colliery. If the coal is of equal quality and price at pithead, from which colliery should the purchases be made?