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Find r if P (20,r)=13.P(20,r-1). |
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Answer» SOLUTION :`""^20P_r=13xx""^20P_(R-1)` `or,(20!)/((20!-r)!)=13xx(20!)/((20-r+1)!)` `or,(20-r)! =((21-r)(20-r)!)/(13)` `or,21-r=13` `or,r=8` |
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