Jackie has two solutions that are 2 percent sulfuric acid and 12 percent sulfuric acid by volume, respectively. If these solutions are mixed in appropriate quantities to produce 60 liters of a solution that is 5 percent sulfuric acid, approximately how many liters of the 2 percent solution will be required?

A:18

B:20

C:24

D:36

E:42

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正确答案： E:42

题目：Jackie有两种溶液，一种含2%的硫酸，另一种含12%的硫酸。假设他将这两种硫酸以一定的比例混合，得到含5%硫酸的溶液60公升，问含2%硫酸的溶液大概需要多少公升？

解：假设需要含2%硫酸的溶液x公升，含12%硫酸溶液y公升，则x+y=60；2%x+12%y=5%*60，简化为2x+12y=300.即x+6y=150；将这两个等式结合计算出x=42，y=18.因此答案为E。