方法(1)设课桌的价钱是x元,由“课桌的价钱×(1+ 5 7 )=一套课桌椅的价钱”得,(1+ 5 7 )x=105 12 7 x=105 x=61.25;105-61.25=43.75(元);方法(2)105-105÷(1+ 5 7 )=105-105÷ 12 7 =105-61.25=43.75(元);方法(3)105÷(5+7)×5=105÷12×5=8.75×5=43.75(元);答:椅子的价钱是43.75元.