If 20 rabbits can be exchanged for 2 sheep, 8 sheep can be exchanged for 2 pigs, and 8 pigs can be exchanged for 2 cows, how many rabbits can be exchanged for 4 cows?
如果20只兔子可以换2只羊，8只羊可以换2头猪，8头猪可以换2头牛，那么用4头牛可以换多少只兔子．
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">10 * 16</gadget>
<output>160</output>

<result>160</result>