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B) Attempt any one.i) Find n if "Ps - 420"Ps)

Answer»

ⁿP₅=42×ⁿP₃or, n!/(n-5)!=42×n!/(n-3)!or, 1/(n-5)!=42/(n-3)(n-4)(n-5)!or, 1=42/(n²-3n-4n+12)or, n²-7n+12=42or, n²-7n-30=0or, n²-10n+3n-30=0or, n(n-10)+3(n-10)=0or, (n-10)(n+3)=0Either, n-10=0or, n=10Or, n+3=0or, n=-3∵, n can not be negative ;∴, n=10 Ans.

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