After the clothes are rubbed with soap and rubbed fully, they are wrung out and "dried", assuming that the clothes still contain 1 kg of dirt. Now rinse twice with 18 kg of water (there is only 18 kg of water in total), and the dirt can be reduced to the original amount at least after the two washes.
衣服在擦好肥皂揉搓充分后再拧"干"，设衣服中还含有污物1千克．现在用18千克清水漂洗两次(总共只有18千克清水)，两次清洗后污物最少能减少到原来的多少．
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * (1/10)</gadget>
<output>1/100 = around 0.01</output>

<result>1/100 = around 0.01</result>