题目
A 60 litre mixture of sugar and water contains sugar and water in the ratio 2:3. How many litres of the mixture should be replaced by sugar so that the ratio of sugar and water becomes 1:1?
解析
一个60升糖和水的混合物,其中糖和水的比例为2:3。需要用糖替换多少升该混合物,才能使糖和水的比例变为1:1?
已知混合物总量为\(60\)升,糖和水的比例为\(2:3\),那么总共的份数为\(2 + 3=5\)份。
每份的量为\(60\div5 = 12\)升。
所以初始糖的量为\(12\times2=24\)升,水的量为\(12\times3 = 36\)升。
设需要替换\(x\)升混合物
替换后糖的量为\((24-\frac{2}{5}x + x)\)升,水的量为\((36-\frac{3}{5}x)\)升。
因为替换后糖和水的比例为\(1:1\),所以可得方程:
\(24-\frac{2}{5}x+x=36-\frac{3}{5}x\)
\(24+\frac{3}{5}x=36-\frac{3}{5}x\)
\(\frac{3}{5}x+\frac{3}{5}x=36 - 24\)
\(\frac{6}{5}x=12\)
\(x = 10\)
所以应该用糖替换\(10\)升该混合物,答案是B。