Question 821235
Let s = son's age
Let m = mother's age
let f = father's age
:
Write an equation for each statement; arrange equations to get it in terms of m:
:
What is a son's age if his mother is twice his age
m = 2s
divide both sides by 2
s = .5 m
:
 and she is 5 years younger than his father.
m = f-5
add 5 to both sides
f = m+5

:
 Added together, the son, mother and fathers ages add up to 100.
s + m + f = 100 
replace s * f
.5m + m + m+5 = 100
2.5m = 100 - 5
 2.5m = 95
 m = 95/2.5
 m = 38 is Mom's age
I'll let you find s and f, check that they add up to 100