4. The demand for an expensive spare part of a passenger jet is 0, 1,2, or 3 units per month with probabilities .2, .3, .4, and .1, respectively. The airline maintenance shop starts operation with a stock of 5 units, and will bring the stock level back to 5 units immediately after it drops below 2 units.

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(a) Devise the procedure for sampling demand.

(b) How many months will elapse until the first replenishment occurs? Use successive values of R from the first column in Table 16.1.