Among the 50 students, 10 have ballpoint pens, 45 have pencils, 1 has neither type of pen, and how many have both types of pens?
50个学生中带圆珠笔的有10人，带铅笔的有45人，两种笔都没有带的有1人，两种笔都带的有几人？
<gadget id="calculator">10 + 45</gadget>
<output>55</output>

<gadget id="calculator">50 - 1</gadget>
<output>49</output>

<gadget id="calculator">55 - 49</gadget>
<output>6</output>

<result>6</result>