Question 293668
There are 7 books numbered 1–7 on the summer reading list. Peter randomly 
chooses 2 books. What is the probability that Peter chooses books numbered 1 and 2? 
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Books 1 and 2 form one group.
There are 7C2 = (7*6)/(1*2) = 21 groups of two
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P(choosing the 1,2 group) = 1/21
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Cheers,
Stan H.