甲乙比为5:2,则甲总数的5/7,乙占总数的2/7
12÷[5/7×(1-20%)-(2/7+5/7×20%)]
=12÷[4/7-3/7]
=84吨,
甲:84×5/7=60吨
乙:84×2/7=24吨