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# Fred is 3 years older than his sister mary, in 7 years she will be six-sevenths of his age. how old are they?

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Preliminary algebra problem really!
Let Fred and Mary be denoted by F and M respectively
Mary being x years old.
Therefore, M=x and F=x+3
In 7 years time, M=x+7 and F=x+3+7
Now, given that M is 6/7th years as old as F seven years later,
M=(6/7)(F), which becomes M=(6/7)(x+10) {EQUATION 1}
Equating EQUATION 1 with M=x+7 and solving for x gives x=11
Therefore Mary is 11 years old while Fred is 11+3, 15 years old (Seven years ago).

Posted on Jun 03, 2012

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Fred is 14 and Mary is 11

Posted on Jun 08, 2011

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Hi.

Algebra !!!!! can't stand it.

Anyway here is the answer >>>>>

Mary is 11 and Fred is 14

Regards.

Posted on Jun 08, 2011

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Fred = Mary +3
7*mary = 6/7 *Fred
substitute fred =mary + 3
7m = 6/7 * (mary + 3) 7m = 6/7*m + 6/7*3 7m - 6/7*m = 6/7*3 m(7-6/7)= 6/7*3
m = (6/7*3) / (7-6/7) m=0.419 years old
substitue m into fred = mary+3 Fred = 3.419 Years old

Posted on Jun 08, 2011

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## Related Questions:

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Let Adjoa's age be x and Kwame's y.
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• Seven years ago sum of their ages was 13: (x-7)+(y-7)=13
• Now you substitute first equation into second equation: (y+3-7)+(y-7)=13
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Let x be Diophantus' age when he died.

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Let Tom's age = X
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From the given facts:

X = 5Y

and

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Please take the time to rate this answer
Many Thanks Don.

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Let the brother's age be x:
16years for Mary = 4x years for Brother

From equation: 4x = 16
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Mary Brother
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Or by calculation;

If 4 is the age for the brother, when the sister is 16, and y years will pass for the to be such that the sister is twice as old as the brother, then;

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Three unknowns with three equasions:
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