Secondly, Xiao Wang's loss was cheated by a swindler who bought shoes with fake money, because the swindler cheated Xiao Wang of a pair of shoes and 20 yuan's change, so accurately speaking, Xiao Wang's loss was a pair of shoes and 20 yuan's change.
As for the question, "How much did Xiao Wang lose in this transaction?" If the shoes are calculated according to the purchase price, Xiao Wang's loss is: 20+20=40 yuan; If the shoes are calculated according to the selling price, Xiao Wang's loss is: 20+30=50 yuan.
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