Algebra

 

               Real numbers a and b satisfy  
               a + ab = 250  
               a - ab = -240  
               Enter all possible values of a, separated by commas.     

 

               Really?  Just add them together.....   

 

               a + ab  =    250    

               a – ab  =  –240    

 

               2a  =  10    

                 a  =  5    

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