GMAT
题目
Jay’s age is twice the age of her daughter Mary today. Four years later, Jay's age will be twice the age of her son Hans at that time. If Jay is 20 years older than Hans today, what will be the age of Mary four years later?
解析
设玛丽的年龄为\( x \)
杰伊的年龄 = 玛丽年龄的两倍 = \( 2x \)
汉斯的年龄 = 比杰伊小20岁 = \( 2x - 20 \)
4年后，杰伊的年龄 = \( 2x + 4 \)，汉斯的年龄 = \( 2x - 20 + 4 = 2x - 16 \)
此时的关系是：杰伊的年龄将是汉斯的两倍，即\( 2x + 4 = 2*(2x - 16) \)
求解\( x \)：
\( 2x + 4 = 4x - 32 \)
\( 2x = 36 \)
\( x = 18 \)
4年后玛丽的年龄 = \( 18 + 4 = 22 \)
选项C
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