a manager is going to purchase new processing equipment and must decide on the number of spare parts to order with the new equipment. the spares cost $200 each, and any unused spares will have an expected salvage value of $50 each. the probability of usage can be described by the following distribution: number 0 1 2 3 probability .1 .5 .25 .15 if a part fails and a spare is not available, two days will be needed to obtain a replacement and install it. the cost for idle equipment is $500 per day. what quantity of spares should be ordered and what is the corresponding expected cost?