he mass transit district of Boston has won a grant of $50 million from the US Department of Transportation to improve its system. The CEO of the Boston MTD must decide where to invest the grant money: in the train system, in the bus network, or in improving th sidewalks. She has the following information about the commuters: . 10% of use all three transport modes: they use the train, the bus and also walk. A total of 50% of the commuters use the bus