# Joint probability mass function

1) Suppose that 3 balls are chosen without replacement from an urn consisting of 5white and 8 red balls. Let Xi equal 1 if the ith ball selected is white, and let it equal 0 otherwise. Give the joint probability mass function of

(a) X1, X2; (b) X1, X2, X3.

2) A bin of 5 transistors is known to contain 2 that are defective. The transistors are to be tested, one at a time, until the defective ones are identified. Denote by N1 the number of tests made until the first defective is identified and by N2 the number of additional tests until the second defective is identified; find the joint probability mass function of N1 and N2.

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#### Solution Summary

The solution calculates joint probability mass function.

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