20 chickens and 16 ducks were kept in two cages, weighing 88 kg in total. If 4 chickens are taken out from the two cages and exchanged with each other, and the weight of the two cages is equal at this time, how much is each chicken lighter than each duck?
有20只鸡和16只鸭子被分别关在两个笼子里，共重88千克．如果从两个笼子里分别取出4只互相交换，这时候两笼重量相等，每只鸡比每只鸭轻多少千克？
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