Mom knits a sweater, the sweater was knitted in the first week (1/4), and the sweater was knitted in the second week (2/5), what fraction of this sweater is left?
妈妈织毛衣，第一周织了毛衣的(1/4)，第二周织了毛衣(2/5)，还剩这件毛衣的几分之几？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/4) - (2/5)</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>