SOLUTION: Dave is 4 years older than Billy. Billy is 3 times older than Jon. All three of their ages combined is 39. What is the age of each child? I started the problem by trying to f

Question 705286: Dave is 4 years older than Billy. Billy is 3 times older than Jon. All three of their ages combined is 39. What is the age of each child?
I started the problem by trying to figure out Jon's age. I came up with the answer of 7. That does not add up correctly. It looks the answer should be 5. I need the steps to get to 5. Trying to help my son with this problem last night and I am stumped.
Thanks
Found 2 solutions by josmiceli, Stitch:
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
Let = Billy's age
Let = Jon's age
Let = Dave's age
given:
(1)
(2)
(3)
--------------------
(2)
Substitute (1) and (2) into (3)
(3)
(3)
Now multiply both sides by
(3)
(3)
(3)
(3)
and, since
(1)
(1)
(1)
and
(2)
(2)
(2)
Billy's age is 15
Jon's age is 5
Dave's age is 19
--------------
check answers
(3)
(3)
(3)
OK

Answer by Stitch(470) (Show Source): You can put this solution on YOUR website!
Let B = Billy's Age
Let D = Dave's Age
Let J = Jon's Age
Equation 1:
Equation 2:
Equation 3:
--------------------------------
Rewrite equation 2 so that it is solved for J

Now both equation 1 and equation 2 are in terms of B
Substitue those values into equation 3 for the same letter.
Equation 3:

Multiply everything by 3 to remove the denominator

Combine like terms

Subtract 12 from both sides

Divide both sides by 7

Now plug 15 into the equations 1 and 2 for B.
---------------------------------------------
Equation 1:

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