Hi

420 more red marbles than blue marbles

Let x and (x +420)represent the amount of blue and red respectively

Question Sets Up the Proportion

      |Cross Multiplying to solve

      7x = 3(x+420) 

      4x = 1260

       x = 315, blue marbles and 735 red marbles  (315+420)



CHECKING our Answer***

 735/315 = 7/3 

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