There is a mid-term exam for a class in the fifth grade of elementary school. The average score of mathematics is 70 points. It is known that the number of passing students is 4 times the number of failing students. The average score of passing students is 80 points. What is the average score of failing students?
小学五年级某班一次期中考试，数学的平均分为70分，已知及格学生人数是不及格人数的4倍，及格学生的平均分为80分，不及格学生的平均分是多少？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">80 * (4/5)</gadget>
<output>64</output>

<gadget id="calculator">70 - 64</gadget>
<output>6</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">6 / (1/5)</gadget>
<output>30</output>

<result>30</result>