InterviewSolution
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InterviewSolution
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If ` ""^(15)P_(r-1): ""^(16)P_(r-2)=3:4`, find r. |
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Answer» Correct Answer - r = 14 `(15!)/({15-(r-1)}) :(16!)/({16-(r-2)})=3:4 rArr (15!)/((16-r)!):(16!)/((18-r)!)=3:4.` ` therefore (15!)/((16-r)!) xx ((18-r)!)/(16!) =(3)/(4) rArr (15!)/((16-r)!)xx((18-r)(17-r)*[(16-r)!])/(16xx(15!))=(3)/(4).` ` therefore (18-r)(17-r)=12 rArr r^(2) -35r+294=0 rArr (r-14)(r-21)=0 rArr r =14 " "[ because r ne 21].` |
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