Two people participate in the competition, A gets wrong questions (1/3) of the total number of questions, B gets 6 questions wrong, both of them get wrong questions (1/5) of the total number, and both get right questions How many ways are there?
两人参加竞赛，甲做错的题目占总数的(1/3)，乙做错了6道题，两人都做错的题目占总数的(1/5)，两人都做对的题有多少道．
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">15 * (1/3)</gadget>
<output>5</output>

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

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

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

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

<gadget id="calculator">15 - 2 - 3 - 3</gadget>
<output>7</output>

<result>7</result>