Permutation

CPT 7797 views 5 replies

The value of Σ r = 1 to 10 r.rPr = ?

 

Quantitative Aptitude  -  Ex - 5 (B) Q. 12 Page No. 5.14

Ans. 11 P  11 - 1

 

Kindly explain in detail

 

Thank you !

Replies (5)

rPr = r! now r*r! can be written as (r+1-1)*r!

= (r+1)*r! – r!

=(r+1)! – r!

1*1P1 = 2! – 1!

2*2P2 = 3! – 2!

3*3P3 = 4! – 3!

So on

By adding all of them we get ultimately 11! -1

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Can't understand. Can someone explain clearly?


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