He can buy 12 artichokes because 15 / 1.25 = <<15/1.25=12>>12
Each artichoke makes 5/3 ounces of dip because there are 3 artichokes per 5 ounces
He can make 20 ounces of dip because 12 x (5/3) = 60/3 = <<12*(5/3)=20>>20
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