Question 984634: Mary, who is sixteen years old, is four times as old as her brother. How old will Mary be when she is twice as old as her brother?
Found 3 solutions by Timnewman, macston, MathTherapy:
Answer by Timnewman(323)   (Show Source):
Answer by macston(5194)  (Show Source):
You can put this solution on YOUR website! .
M=Mary's age=16 yrs; B=brothers age; X=number of years until Mary is twice as old
M=4B
16 yrs=4B
4yrs=B Brother is 4 years old.
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M+X=2(B+X)
16yrs+X=2(4yrs+X)
16yrs+X=8yrs+2X
8yrs=X In 8 years Mary will be twice as old as brother.
M+8yrs=16yrs+8yrs=24yrs
ANSWER: Mary will be 24 years old when she is twice as old as her brother.
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CHECK:
16yrs+8yrs=2(4yrs+8yrs)
24yrs=2(12yrs)
24yrs=24yrs
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In 8 years, Mary will be 24 and brother will be 12.
Answer by MathTherapy(10552)  (Show Source):
You can put this solution on YOUR website! Mary, who is sixteen years old, is four times as old as her brother. How old will Mary be when she is twice as old as her brother?
In 8 years' time, Mary will be  , and will be twice her brother's age, then.
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