Question 418743
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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
  {{{7/3 = (x+420) /x}}}    |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