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Question Number 151485 by liberty last updated on 21/Aug/21
Answered by iloveisrael last updated on 21/Aug/21
$$\:{N}\left({A}\right)=\:\frac{\mathrm{5}!}{\mathrm{3}!}×\frac{\mathrm{7}!}{\mathrm{2}!}\:=\:\frac{\mathrm{120}}{\mathrm{6}}\:×\frac{\mathrm{5040}}{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:=\:\mathrm{20}×\mathrm{2520}=\mathrm{50400} \\ $$