Xiaohua investigated the presents that all the classmates gave their mothers on Mother's Day. (1/4) students sent flowers, (1/5) students sent greeting cards, and the rest of the students sent a picture drawn by themselves. What percentage of the class did the students who sent the picture account for?
小华调查了全班同学母亲节那天送给妈妈的礼物．(1/4)的同学送鲜花，(1/5)的同学送贺卡，其余同学送的是自己画的一张画，送画的同学占全班人数的几分之几？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/4) - (1/5)</gadget>
<output>11/20 = around 0.55</output>

<result>11/20 = around 0.55</result>