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  3. When David is twice as old as he is now he will be four times as old as his daug

When David is twice as old as he is now he will be four times as old as his daug

游客2023-10-17  13
问题 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 year’s time.If in 1990, four years ago, he was four times as old as his daughter, in what year was she born?
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答案 In 1983
解析 分析题目 可知，四年前为1990年，那么今年为1994年。假设David的女儿今年X岁,David今年Y岁，由此可列二元一次方程组:4（X +5）=2Y;4（X-4）=Y-4。解方程组可得:X=11,Y =32,即Jane今年11岁,David今年32岁,那么1994-11 = 1983。由此可知Jane出生于1983年。
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