The required answer is,
\(P(7, 4) \times P(6, 3)=100800\\P(5,4)=120\)
The given expression is,
\(P(7, 4) \times P(6, 3)\\P(5,4)\)
Permutation: Basically, Permutation is an arrangement of objects in a particular way or order. While dealing with permutation one should concerned about the selection as well as arrangement.
The formula of permutation is,
\(P(n,r)=\frac{n!}{(n-r)!}\)
Simplifying the first expression.
\(P(7,4)\timesP(6,3)=\frac{7!}{(7-4)!} \times\frac{6!}{(6-3)!} \\=\frac{7!}{3!}\times\frac{6!}{3!} \\ =\frac{7\times6\times5\times4\times3\times2\times1}{3\times2\times1}\times\frac{6\times5\times4\times3\times2\times1}{3\times2\times1} \\ =7\times6\times5\times4\times6\times5\times4\\=840\times120\\=100800\\\)
Again solving the second expression.
\(P(5,4)=\frac{5!}{(5-4)!} \\=5!\times1!\\=5\times4\times3\times2\times1\\=120\)
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