Answer:
14
Step-by-step explanation:
The sum of their age is 19.
This means that when you add their ages together, it will be 19.
L+R=19
The positive difference of their age is 9.
It tells you that Lily is the older child.
Since the difference is a positive number, that means it would be Lily's age minus Rosie's age since Lily is older.
L-R=9
Now you have 2 equations that can be used to find their ages.
Start with the first equation.
L+R=19.
Solve for L.
Subtract R on both sides.
L=19-R
Now use the substitution method (replacing or "substituting" L with 19-R) for the next equation.
L-R=9
(19-R)-R=9
19-2R=9
-2R=-10
R=5
Rosie's age is 5.
Rosie's age is 5. Now use the first equation to find Lily's age.
L+5=19
L=14.
Lily's age is 14.
