Use the method of Example 9.5.10 to answer the following questions. (a) How many 18-bit-strings contain exactly eight 1's? The number of 18 -bit strings that contain exactly eight. 1 's equals the number of ways to choose the positions for the 1 's in the string, namely, (b) How many 18 -bit strings contain at least fifteen 1 's? _____
(c) How many 18-bit strings contain at least one 1 ? _____
(d) How many 18 -bit strings contain at most one 1?
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