一到英语竞赛智力题,When David is twice as old as he is now he will be

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一到英语竞赛智力题,
When David is twice as old as he is now he will be four times as old as his daughter Jane will be in five years time.If in 1990,he was four times as old as his daughter; in what year was she born?答案是1983年,我求到的是1975年,不理解

你漏了个 four years ago,我的神啊
when david is twice as old as he is now he will four times as old as his daughter Jane will be in five years time .If in 1990,four years ago,he was four times as old as his daughter ,in what year was she born?
当david的年龄是现在年龄的两倍的时候,他的年龄是他的女儿jane五年后年龄的四倍.如果在1990年,四年前,他的年龄是他女儿年龄的四倍,那么jane是什么时候出生的?
设现在david年龄x,他的女儿jane的年龄y,则2x=4(y+5)
1990年是4年前,则现在是1994年
所以根据第二句话有：x-4=4(y-4)
则根据以上两个方程求出y=11,x=32
则在1994年也就是现在他爸爸32岁,他女儿11岁,
则四年前他女儿11－4＝7岁
则他女儿出生在1990－7＝1983年

一到英语竞赛智力题,When David is twice as old as he is now he will be 一个英语竞赛智力题When David is twice as old as he is now he will be when David is twice as old as he is now he will be four time when david is twice as old as he is now he will four times a the man is now twice as old as the woman was when he was old Fred is 24 and twice as old as Ginger was when he was as old that's easy,Bob is twice as old as jack,so he is now thirty. Jsck is twice as old as Jill,but in five years time he will Jack is twice as old as Jill ,but in five years time he will In 15 years she will be twice as old as her son.How old is s How old will i be when i am twice as old as my brother? Jack is twice as old as Jill,