4.2.20. Suppose a radioactive source is metered for two hours, during which time the tota l number of alpha particles coun ted is 482. What is the probability t hat exactly three particles will he counted i n the nex t two mi nutes? A nswer the question two ways--first, by defining *X *to be the num ber of particles coun ted in t wo minutes, and second, by defining *X *to be the number of particles counted in one minu te.

4.2.21. Suppose Lhat on-the-job in.iuries in a texti le mill occur at the rat e of 0.1 per day.

(a) What is t he probabili ty that two accidents will occur during the next (five-day) work week?

(b) Cs the probability that four acciden ts will occur over the next two work weeks t he square of your answer to Part (a)? Explain.

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