4 years ago the father was 7 times older than his son. After 4 years he will be 3 times older than his son. How old is the son, how old is the father? FAST!!!!

Mihail
Apr 3, 2015

#1**+15 **

Father's age = f, son's age = s

f - 4 = 7(s - 4) Four years ago (1)

f + 4 = 3(s + 4) Four years hence (2)

From (1) we have f - 4 = 7s - 28 or f = 7s - 24 (3)

From (2) we have f + 4 = 3s + 12 or f = 3s + 8 (4)

From (3) and (4): 7s - 24 = 3s + 8 or 4s = 32 so s = 8

Put this back into (4) to get f = 3*8 + 8 or f = 32

Father's age now is 32

Son's age now is 8

.

Alan
Apr 3, 2015

#1**+15 **

Best Answer

Father's age = f, son's age = s

f - 4 = 7(s - 4) Four years ago (1)

f + 4 = 3(s + 4) Four years hence (2)

From (1) we have f - 4 = 7s - 28 or f = 7s - 24 (3)

From (2) we have f + 4 = 3s + 12 or f = 3s + 8 (4)

From (3) and (4): 7s - 24 = 3s + 8 or 4s = 32 so s = 8

Put this back into (4) to get f = 3*8 + 8 or f = 32

Father's age now is 32

Son's age now is 8

.

Alan
Apr 3, 2015

#2**+5 **

We can also do this with one variable.

Let x be the son's age 4 years ago,

Then his father's age 4 years ago = 7x

And years later, - 4 years from now - the father will be 3 times older than his son. So we have.....

3(x + 8) = 7x + 8 simplify

3x+ 24 = 7x + 8

4x = 16

So the son's age 4 years ago was 4

And his father was 7(4) = 28

And 4 yeara later the son is 8 and the father is 32.

CPhill
Apr 3, 2015