Dana has 15 more pencils than Jayden who has 20, so Dana has 20+15 = <<20+15=35>>35 pencils
Jayden has 20 pencils which is twice as much as Marcus's so Marcus has 20/2 = <<20/2=10>>10 pencils
Dana has 35-10 = <<35-10=25>>25 more pencils than Marcus
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