He starts with 4 blue marbles because 10 x .4 = <<10*.4=4>>4
60% of the marbles are red because 100 - 40 = <<100-40=60>>60
He has 6 red marbles because 10 x .6 = <<10*.6=6>>6
He trades 5 red marbles because 6 - 1 = <<6-1=5>>5
He gets 10 blue marbles because 5 x 2 = <<5*2=10>>10
He has 15 marbles now because 4 + 1 + 10 = <<4+1+10=15>>15
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