SOLUTION: Can you please help me answer this? Mark is 11 years older than his sister. In 8 years he will be twice as old as she will be then. How old art they now?

Algebra ->  Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: Can you please help me answer this? Mark is 11 years older than his sister. In 8 years he will be twice as old as she will be then. How old art they now?      Log On


   

Question 526700: Can you please help me answer this?
Mark is 11 years older than his sister. In 8 years he will be twice as old as she will be then. How old art they now?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
let m = Mark's present age
let s = sister's present age
:
Write an equation for each statement:
:
"Mark is 11 years older than his sister."
m = s+11
:
"In 8 years he will be twice as old as she will be then."
m + 8 = 2(s+8)
m + 8 = 2s + 16
m = 2s + 16 - 8
m = 2s + 8
Replace m with (s+11), from the 1st statement
s + 11 = 2s + 8
11 - 8 = 2s - s
3 = s
s = 3 yrs is the sisters age
then
3 + 11 = 14 is Marks age
:
:
See if the checks out in the statement:
"In 8 years he will be twice as old as she will be then."
14 + 8 = 2(3+8)
22 = 2(11)