Teacher Liu brought 1,000 yuan to buy chalk. I bought 20 boxes of chalk, leaving 160 yuan. How much does each case of chalk cost?
刘老师带1000元买粉笔．买了20箱粉笔，剩下160元．每箱粉笔的价钱是多少？
<gadget id="calculator">1_000 - 160</gadget>
<output>840</output>

<gadget id="calculator">840 / 20</gadget>
<output>42</output>

<result>42</result>