If Chris and Ryan put together their marbles in a pile, the pile will have 12+28 = <<12+28=40>>40 marbles.
If they then take 1/4 of the marbles each, every person will receive 1/4*40 = <<1/4*40=10>>10 marbles.
Both of them will have taken a total of 10+10 = <<10+10=20>>20 marbles.
The number of marbles remaining in the pile is 40-20 = <<40-20=20>>20
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