<PRE><B>Question 518918</B>
Let
Present age of Man = m
Present age of Son = s


Man is 4 times as old as his son. 
m=4s.............(1)

20 years later 
Man age = m+20
Son age = s+20

Then he will be just twice as old as his son.
m+20=2(s+20)
m+20=2s+40
m=2s+40-20
m=2s+20..............(2)

Put the value of m from (1) to (2)

4s=2s+20
4s-2s=20
2s=20
2s/2=20/2
s=10
Put the value of s in (1)
m=4s
m=4(10)
m=40


Present age of Man = m = 40 years old
Present age of Son = s = 10 years old

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