Question 428147
The Faber Family has 3 children.
: 
Write an equation for each statement:
:
Bill's age plus Mike's age add to 20 years.
b + m = 20
:
 Mike's age plus Sally's age add to 29 years.
m + s = 29
:
 Bill's age plus Sally's age add to 23 years.
b + s = 23
b = (-s + 23)
:
In the 1st equation, replace b wtih (-s + 23)
(-s + 23) + m = 20
-s + m = 20 - 23
-s + m = -3
:
Add the above equation to the 2nd equation
-s + m = -3
 s + m = 29
-------------- addition eliminates s, find m
2m = 26
m = 13 yrs is Mike's age
then
b + 13 = 20
b = 20 - 13
b = 7 yrs is Bill's age
and
7 + s = 23
s = 23 - 7
s = 16 is Sally's age
:
" The difference in age between the old child and young child is what?
16 - 7 = 9 yrs is the diff from oldest and youngest