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The number of ways in which we can select fournumbers from 1 to 30 so as to exclude every selection of four consecutivenumbers isa. `27378`b. `27405`c. `27399`d.none of theseA. 27378B. 27405C. 27399D. none of these |
Answer» The numbre of ways of selecting any four numbres from 1 to 30, is `""^(30)C_(4)`. Four consecutive numbers can be chosen in the following ways : (1, 2, 3, 4),(2, 3, 4, 5),…….,(27, 28, 29, 30). Thus, required number of ways `=""^(30)C_(4)-27=27378`. | |