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If ."""^(n + 2) P(4) = 42 xx ."""^(n)P(2...

If `."""^(n + 2) P_(4)` `= 42 xx ."""^(n)P_(2)` find n .

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The correct Answer is:
`rarr (n + 2) (n + 1) = 42 = 7 xx 6 rArr n + 2 = 7 rArr n = 5`
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