Question 984634
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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.