SOLUTION: mark is 11 years older then his sister. in eight years he will be twice as old as she will be. how old are they now?

Question 611414: mark is 11 years older then his sister. in eight years he will be twice as old as she will be. how old are they now?
Answer by radh(108) (Show Source): You can put this solution on YOUR website!
Let's write this mathematically. We'll represent age by x.
Mark is 11 years older than his sister (11+x). In eight years (+8) he will be twice as old as his sister (2x).
So, it'd be:
Let's simplify that:
Now we know that x=3, so we plug it back into the original formula: , so Mark is 14 and his sister is 3. :)
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