Question 1112339
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The simplest way to solve this equation is to find in the Internet the 11-th row of the Pascal's triangle.


I found it at this link

http://jwilson.coe.uga.edu/EMAT6680Su12/Berryman/6690/BerrymanK-Pascals/BerrymanK-Pascals.html



and found the value of  r= 3  in this way.


The last step is to check this solution:  {{{C[10]^3}}} = {{{(10*9*8)/3!}}} = 10*3*4 = 120.              ! Correct !
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Solved.