If one pen can be exchanged for 5 ballpoint pens, and 4 ballpoint pens can be exchanged for 10 pencils, then how many pencils can be exchanged for 4 pens?
一枝钢笔能换5枝圆珠笔，4枝圆珠笔能换10枝铅笔，那么4枝钢笔能换多少枝铅笔．
<gadget id="calculator">4 / 4</gadget>
<output>1</output>

<gadget id="calculator">5 * 1</gadget>
<output>5</output>

<gadget id="calculator">10 * 5</gadget>
<output>50</output>

<result>50</result>