There are three kinds of paper cups, which can hold (1/3) liters, (4/7) liters and (1/5) liters respectively. Xiao Ming poured a bottle of 2 liters of juice into one of the paper cups, about 4 cup. How many liters of paper cups does Xiao Ming use?
有三种纸杯，分别能装(1/3)升、(4/7)升与(1/5)升，小明把一瓶2升的果汁倒入了其中的一种纸杯种，大约倒了4杯．小明用的是多少升的纸杯．
<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>