Xiaohua's class has conducted 4 math tests, and the results are getting better and better. In the first test, 70% of the candidates scored more than 80 points; in the second test, 75% of the candidates scored more than 80 points; in the third test, 85% of the candidates scored more than 80 points; in the fourth test, 90% Candidates scored more than 80 points in the test; then what is the percentage of students whose scores are above 80 points in the four tests?
小华所在的班级进行了4次数学测验，成绩越来越好．第一次测验有70%的考生考了80分以上；第二次测验有75%考生考了80分以上；第三次测验有85%生考了80分以上；第四次测验有90%考生考了80分以上；那么四次测验成绩都在80分以上的学生的百分比至少是多少．
<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</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">(3/4) - (3/10)</gadget>
<output>9/20 = around 0.45</output>

<gadget id="calculator">1 - (9/20)</gadget>
<output>11/20 = around 0.55</output>

<gadget id="calculator">(17/20) - (11/20)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">(9/10) - (7/10)</gadget>
<output>1/5 = around 0.2</output>

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