SOLUTION: Find the sum of the series 15/42+15/56+15/72+15/90+…+15/9900

The series is 15 times  S = 


Each addend in the sum S is


     =          (1)

     =        
    
     = 

     = 

       . . . and so on . . . 

     =      (last)


The pattern is clear.


When you add the lines from (1) to the (last),  all  intermediate terms with opposite signs will cancel each other, 

leaving only   =  = .


So the ANSWER to the problem's question is   =  =  = 2.35.