In a knowledge contest, two people, A and B, successfully entered the finals. In the finals, there were ten rush-answer questions, 20 points for each correct answer, and 10 points for each wrong answer. All ten questions were answered by two contestants. Answer 3 questions quickly, B gets 50 points, how many questions does B get wrong?
在一次知识竞赛中，甲，乙二人成功杀入总决赛，总决赛共十道抢答题，答对一题20分，答错一题扣10分，十道题全被两位选手抢答，甲抢答3道题，乙得到50分，乙答错几道题？
<gadget id="calculator">10 - 3</gadget>
<output>7</output>

<gadget id="calculator">20 * 7</gadget>
<output>140</output>

<gadget id="calculator">140 - 50</gadget>
<output>90</output>

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

<gadget id="calculator">90 / 30</gadget>
<output>3</output>

<result>3</result>