A competition, a total of 10 questions, 10 points for 1 correct answer, 5 points for each wrong answer or no answer, obviously scored 70 points in this test, how many questions did he answer correctly?
一次竞赛，共10题，答对1题记10分，答错或是不答每题倒扣5分，明明在这次测试中得分70分，他答对了几道题？
<gadget id="calculator">10 * 10</gadget>
<output>100</output>

<gadget id="calculator">100 - 70</gadget>
<output>30</output>

<gadget id="calculator">10 + 5</gadget>
<output>15</output>

<gadget id="calculator">30 / 15</gadget>
<output>2</output>

<gadget id="calculator">10 - 2</gadget>
<output>8</output>

<result>8</result>