If 10 rabbits can be exchanged for 1 sheep, and 4 sheep can be exchanged for 2 pigs, then how many rabbits can be exchanged for 4 pigs?
如果10兔换1只羊，4只羊可换2头猪，那么4头猪可换多少只兔．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 * 10</gadget>
<output>20</output>

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>