The school held a quiz contest, with a total of 10 rush-answer questions. It is stipulated that 10 points will be awarded for each correct answer, and 20 points will be deducted for each wrong answer. Fanfan scored 40 points for answering 10 questions. How many questions did Fanfan get right?
学校举行智力竞赛，共出10道抢答题．规定答对一题加10分，答错一题扣20分．凡凡抢答10道题得了40分．凡凡答对了几题？
<gadget id="calculator">10 * 10</gadget>
<output>100</output>

<gadget id="calculator">100 - 40</gadget>
<output>60</output>

<gadget id="calculator">10 + 20</gadget>
<output>30</output>

<gadget id="calculator">60 / 30</gadget>
<output>2</output>

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

<result>8</result>