A certain school held a mathematics competition. There were 10 questions in total. It was stipulated that 10 points would be awarded for each correct answer, and 5 points would be deducted for each wrong answer. Xiaoyu’s score was 70 points. How many questions did he answer correctly? Please write your reason.
某校举行数学竞赛，试题共10道，规定做对一题得10分，做错一题倒扣5分，小宇成绩为70分，问他做对几道题？请写出你的理由．
<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>