If you buy a (21/5) kilogram of watermelon in a beverage store, you can squeeze out (7/5) kilograms of watermelon juice. How many kilograms of watermelon do you need to squeeze 1 kilogram of watermelon juice?
饮料店买一个(21/5)千克西瓜可榨汁(7/5)千克，榨1千克西瓜汁需要多少千克西瓜．
<gadget id="calculator">7 / 5</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">21 / 5</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">(7/5) / (21/5)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / (1/3)</gadget>
<output>3</output>

<result>3</result>