In an exam, the results of A and B are as follows: A answered 1/3 of all the questions wrongly, and B answered 7 questions wrongly. The questions that both A and B get wrong account for 20% of all the test questions. Then there are at least how many questions both A and B can answer correctly.
在一次考试中甲、乙两人考试结果如下：甲答错了全部试题的(1/3)，乙答错了7道题．甲、乙都答错的题目占全部试题的20%．则甲、乙两人都答对的题目最少有多少道．
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">3 * 5 * (1/5)</gadget>
<output>3</output>

<gadget id="calculator">7 - 3</gadget>
<output>4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">3 * 5 * (1/3)</gadget>
<output>5</output>

<gadget id="calculator">5 - 3</gadget>
<output>2</output>

<gadget id="calculator">15 - 3 - 4 - 2</gadget>
<output>6</output>

<result>6</result>