Dexter used 4 x 3/8 = 3/2 liters of paint.
Jay used 4 x 5/8 = 5/2 liters of paint.
Together, they used 3/2 + 5/2 = <<3/2+5/2=4>>4 liters of paint.
Since each of them used a gallon of paint, then they both used 2 x 4 = <<2*4=8>>8 liters of paint together.
Therefore, 8 - 4 = <<8-4=4>>4 liters of paint were left.
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