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If ^10 Pr=5040 , find the value of rdot...

If `^10 P_r=5040 ,` find the value of `rdot`

Text Solution

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`.^(15)P_(r) = 2730`
`rArr (15!)/((15-r)!) = 2730`
`rArr (15 xx 14 xx 13 xx 12!)/((15-r)!) = 15 xx 14 xx 13`
`rArr 12! = (15 - r)!`
`rArr 12= 15 - r`
`rArr r = 3`.
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