Mary, who is sixteen years old, is four times as old as her brother. How old will Mary be when she she is twice as old as her brother?

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Answer 1 · 2016-12-02T08:09:20

#24# years old

When Mary is #16#, her brother is #4#.

Let #x# be the year when Mary will be twice as old as her brother.

#16 + x = 2(4+x)#

#x = 8#

Therefore, Mary will be

#16 + 8 = "24 years old"#

while her brother will be

#4+8 = "12 years old"#