Questions on Algebra: Systems of Linear Equations answered by real tutors!

Algebra ->  Algebra  -> Coordinate Systems and Linear Equations -> Questions on Algebra: Systems of Linear Equations answered by real tutors!     (Log On)
Ad: You enter your algebra equation or inequality - Algebrator solves it step-by-step while providing clear explanations. Free on-line demo .
Ad: Algebra Solved!™: algebra software that solves YOUR algebra homework problems with step-by-step help!

   

Question 154191: Five years ago a man was seven times as old as his son. Five years hence, the father will be three times as old as his son. Find their present ages.: Five years ago a man was seven times as old as his son. Five years hence, the father will be three times as old as his son. Find their present ages.
Answer by josmiceli(2035) About Me  (Show Source):
You can put this solution on YOUR website!
Let f= father's age now
Let s= son's age now
f - 5= father's age 5 years ago
s - 5= son's age 5 years ago
f - 5 = 7*(s - 5)
f - 5 = 7s - 35
f = 7s - 30
------------------
f + 5= father's age in 5 years hence
s + 5= son's age in 5 years hence
f + 5 = 3*(s + 5)
f + 5 = 3s + 15
f = 3s + 10
-----------------
Set the 2 expressions for f equal to eachother
7s - 30 = 3s + 10
4s = 40
s = 10
Now substitute this in one of the equations
f = 7s - 30
f = 7*10 - 30
f = 40
The father is 40 and the son is 10