SOLUTION: Mark is 11 years older than his sister. In 8 years he will be twice as old as she will be then. How old are they now? How do you solve this? Please show me the steps. I have a t

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Question 693525: Mark is 11 years older than his sister. In 8 years he will be twice as old as she will be then. How old are they now?
How do you solve this? Please show me the steps. I have a test tomorrow and I need help.
Answer by ReadingBoosters(3246) (Show Source):
You can put this solution on YOUR website!
m is for Mark
s is for his sister
...
given equations
m = s + 11
m+8 = 2(s+8) ==> adding 8 to both m and s to account for 8 years later
...
substitute m of the first equation into the second
s+11 + 8 = 2(s+8) ==> distribute the 2
s+11 + 8 = 2s + 16 ==> combine like terms
s + 19 = 2s + 16 ==> group s variables on one side
s - 2s = 16 - 19 ==> combine like terms
-s = -3 ==>solve for s
s = 3
...
Mark is 3+11 =
His sister is
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