Among the students in a certain class, 78% like swimming, 82% like painting, 90% like singing, and 70% like playing chess. What is the minimum percentage of students in the class who have these four hobbies at the same time?
某班学生中，78%喜欢游泳，82%喜欢绘画，90%喜欢唱歌，70%喜欢下棋．该班学生中同时有这四种爱好的学生所占的最小百分比是多少．
<gadget id="calculator">78 / 100</gadget>
<output>39/50 = around 0.78</output>

<gadget id="calculator">1 - (39/50)</gadget>
<output>11/50 = around 0.22</output>

<gadget id="calculator">82 / 100</gadget>
<output>41/50 = around 0.82</output>

<gadget id="calculator">1 - (41/50)</gadget>
<output>9/50 = around 0.18</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (11/50) - (9/50) - (1/10) - (3/10)</gadget>
<output>1/5 = around 0.2</output>

<result>1/5 = around 0.2</result>