Question 179529
He invested part of the money at 7% and the rest at 9%.
How much was invested at 7%?    ----->   X
invested part of the money at 7% would made X*0.07
invested part of the money at 9% would made (12,000 - X)*0.09
He made a total of $970 --->  970  =  X*0.07 + (12,000 - X)*0.07

       970  =  X*0.07 + (12,000 - X)*0.09
       970  =  X*0.07 + 1080 - 0.09X
       0.09X-0.07X =   1080 - 970
       0.02X       =    110
           X       =    110/0.02 
                   =    5500

How much was invested at 7%?  $5,500   Ans.