For a bucket of water, use up the whole bucket for the first time (2/5). What percentage of the full barrel is left after using 1/3 of the full barrel for the second time?
一桶水，第一次用去全桶的(2/5)．第二次用去全桶的(1/3)，还剩下全桶的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (2/5) - (1/3)</gadget>
<output>4/15 = around 0.266667</output>

<result>4/15 = around 0.266667</result>