If 1+22∑r=0{r(r+2)+1}⋅r!=k!, then the value of k is
A
12
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B
22
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C
24
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D
32
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Solution
The correct option is C24 1+22∑r=0{r(r+2)+1}⋅r!=1+22∑r=0{(r+1−1)(r+2)+1}r!=1+22∑r=0[(r+2)!−(r+1)!]=1+(2!−1!)+(3!−2!)+⋯+(24!−23!)=1+24!−1!=24!
Therefore, k=24