In an exam, the test results of A and B are as follows, A got wrong (1/3) of all the test questions, B got 7 questions wrong, and the test questions that both A and B got wrong accounted for (1/7) 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题，甲、乙都答错的试题占全部试题的(1/7)，那么甲、乙都答对的试题至少有多少题．
<gadget id="calculator">3 / 1</gadget>
<output>3</output>

<gadget id="calculator">3 * 7</gadget>
<output>21</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">3 * 7 * (1/7)</gadget>
<output>3</output>

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

<gadget id="calculator">3 * 7 * (1/3)</gadget>
<output>7</output>

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

<gadget id="calculator">21 - 3 - 4 - 4</gadget>
<output>10</output>

<result>10</result>