Question 899667
Let a = Sister's age
Let c = C's age
Let g = brother's age 
:
Write an equation for each statement rearrange for substitution in the last equation:

Chris is ten years older than his sister, Alice.
c = a + 10
a = c - 10
 Chris is also twice as old as his brother, Greg.
c = 2g
g = .5c
 How old is Chris if the sum of all three of their ages is 50?
a + c + g = 50
replace a and g
(c-10) + c + .5c = 50
2.5c = 50 + 10
c = 60/2.5
c = 24 yrs old is C's age
then
a = 24 - 10
a = 14 yrs is A's age
and
.5(24) = 12 yrs is G's age
:
Note these add up to 50