In an exam, the statistics of Fang Fang and Yuan Yuan’s exam results are as follows: Fang Fang got wrong (1/3) of all the test questions, Yuan Yuan got 7 questions wrong, and both Fang Fang and Yuan Yuan got wrong answers (1/3). (1/5) of the test questions, then at least how many questions both Fang Fang and Yuan Yuan can answer correctly.
在一次考试中，方方和圆圆考试结果统计如下：方方答错了全部试题的(1/3)，圆圆答错了7道题，方方和圆圆都答错的题目占全部试题的(1/5)，那么方方和圆圆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">1 / 5</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>