数学题:甲乙丙三人的平均年龄为22岁 ，如果甲，乙的平均年龄是18岁，乙，丙的平均年龄是25岁，那么乙的年龄是几岁?

数学题解答：这是一道关于平均数的问题，需要用到关系式“平均数×份数＝总数”。

甲+乙 + 乙+丙 －（甲+乙+丙）＝乙

18×2 + 25×2 – 22×3

=36+50-66

=86-66

=20（岁）

答：乙的年龄是20岁。

用方程解：设乙的年龄是x岁。

22×3 + x = 18×2 + 25×2

66 + x = 86

x = 20

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