Answer
There are 36 combinations and 181440 permutations
Explanation
The number of combinations of n object taking r at a time is given by the formula;
[tex]^nC_r=\frac{n!}{r!(n-r)!}[/tex]
From the question, n = 9 and r = 7, then substitute these values into the formula
[tex]^9C_7=\frac{9!}{7!(9-7)!}=\frac{9!}{7!\text{ }2!}=\frac{9\cdot8\cdot7!}{7!\times2}=\frac{72}{2}=36[/tex]
The number of permutations of n object taking r at a time is given by the formula;
[tex]^nP_r=\frac{n!}{(n-r)!}[/tex]
Also, n = 9 and r = 7, then substitute these values into the formula to get the number of permutations
[tex]^9P_7=\frac{9!}{(9-7)!}=\frac{9!}{2!}=\frac{9\cdot8\cdot7\cdot6\cdot5\cdot4\cdot3\cdot2!}{2!}=181440[/tex]
Therefore, there are 36 combinations and 181440 permutations
