Refer to Exercise 4.91. Suppose the sampling of 3 alternators is done by randomly choosing one after another and without replacement. The event A can then be described as G1G2G3, where G denotes "good" and the suffixes refer to the order of the draws. Use the method of Example 14 to calculate how many ways can there be 4 H's and 7 T's? (Put P(A) and P(B). Verify that you get the same results as in Exercise 4.91.
This illustrates the following fact: To arrive at a random sample, we may randomly draw one object at a time without replacement and then disregard the order of the draws.