数学题:水果店买来两筐苹果，乙筐苹果的个数是甲筐苹果的七分之三；从甲筐中取出39个，放入乙筐，这时乙筐苹果个数就是甲筐的五分之四，乙筐原有多少个苹果？（这个题抓住总数不变，求解）

数学题解答：

由“乙筐苹果的个数是甲筐苹果的七分之三”可知：乙筐苹果是3份，甲筐苹果是7份。两筐一共就是3+7=10份。

乙筐占总数的3/10。

由“这时乙筐苹果个数就是甲筐的五分之四”可知：乙筐苹果是4份，甲筐苹果是5份。一共是9份。

乙筐占总数的4/9。

总数是：39÷(4/9 – 3/10)= 39 ÷ 13/90 = 270（个）

乙筐苹果是：270 × 3/10 =81（个）

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