SOLUTION: A father’s age is four times that of his son. After five years ,it will be three times that of his son. How many more years will take if father’s age is to be twice that of his son

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Question 815464: A father’s age is four times that of his son. After five years ,it will be three times that of his son. How many more years will take if father’s age is to be twice that of his son.

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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Let f = father's present age
let s = son's
:
Write an equation for each statement
:
A father’s age is four times that of his son.
f = 4s
:
After five years ,it will be three times that of his son.
f + 5 = 3(s+5)
f + 5 = 3s + 15
f = 3s + 15 - 5
f = 3s + 10
Replace f with 4s (from the the first statement)
4s = 3s + 10
4s - 3s = 10
s = 10 yrs is son's present age
then
4(10) = 40 yrs is father's age
:
How many more years will take if father’s age is to be twice that of his son.
let y = no. of years, from the present, for this to be true
y + 40 = 2(y + 10)
y + 40 = 2y + 20
40 - 20 = 2y - y
y = 20 yrs from the now father will be twice as old as the son
:
Check this out
40+20 = 2(10+20)