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A father is 9 times as old as his son. In three years, the father will be 6 times as old as his son.

How old is the son?

 Jan 22, 2021
 #1
avatar+41 
+3

I think the son is currently 6 years old. You can plug this answer in and solve the question backwards.

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 Jan 22, 2021
 #2
avatar+165 
0

Close, but not quite.

Let x be the age of the father and let y be the age of the son.

\(x=9y\\ x+3=6(y+3)\\ 9y+3=6y+18\\ 3y=15\\ x=5\)

So the son is actually 5 years old.

textot  Jan 22, 2021
 #3
avatar+267 
+1

use systems of equations

 

the two systems are: 

 

f=9s

f+3=6(s+3)

 

steps: 

1. expand 6(s+3) to get 6s+18

2. substitute f in terms of s (and we know that f=9s, so then the second equation becomes 9s+3=6s+18

3. now we know how to solve. add -6s to both sides, add -3 to both sides, and finally divide both sides by 3. 

 

We get: 

 

f=45, s=5

 

so the son is 5 years old and the father is 45 years old

 Jan 22, 2021

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