Give 10 students pencils, 3 pencils are left over, but 4 pencils are not enough. There are as many leftovers as there are not enough, how many pencils are there.
给10个学生发铅笔，每人3支还剩下一些，每人4支又不够．剩下的和不够的同样多，有多少支铅笔．
<gadget id="calculator">10 * 3</gadget>
<output>30</output>

<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">30 + 5</gadget>
<output>35</output>

<result>35</result>