问题描述：
Helen is twenty years old ,and her age is four times as much as Mary 's.When Helen 's age is twi...
Helen is twenty years old ,and her age is four times as much as Mary 's.When Helen 's age is twice as much as Mary 's ,how old Helen then ?
Helen is twenty years old ,and her age is four times as much as Mary 's.When Helen 's age is twice as much as Mary 's ,how old Helen then ?
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