if 3 books are picked at random from a shelf containing 5 novels,3 books of poems and a dictionary ,in how many ways can be done if the dictionary is selected
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There are three ways to get the dictionary. We have 1 dictionary (d) and 8 non-dictionaries (nd).
Case1. d,nd,nd, its probability is 1/9.
Case 2, nd,d,nd, its probability is (8/9)(1/8)=1/9
Case 3. nd,nd,d, its probability is (8/9)(7/8)(1/7)=1/9
Total is 3*(1/9)=1/3.
(b) There are thee favorable cases here
Case 1. nnp, its probability is (5/9)(4/8)(2/7)=5/63.
Case 2. npn, its probability is (5/9)(2/8)(4/7)=5/63.
Case 3. pnn, its probability is (2/9)(5/8)(4/7)=5/63.
Total is 3 (5/63)=5/21
hope it will help you
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