Question

five year hence,the age of jacob will be three times that of his son.five years ago.jacob's age was seven times that of his son.what is thair present age?

Answer 1

why did u post this in the history section? :o

Answer 2

Anyways,

in 5 years, jacob's age = J+5
in 5 years, his son's age = S+5
but Jacob will be 3 times older than his son, therefore
J+5=3(S+5)
J+5=3S+15
J=3S+10 --------------(equation 1)

5 years ago, jacob's age = J-5
5 years ago, his son's age = S-5
but Jacob was 7 times older than his son, therefore
J-5=7(S-5)
J-5=7S-35
J=7S-30 --------------(equation 2)

this means that
7S-30=3S+10
7S-3S=10+30
4S=40
S=10

this means that from equation 2,
J=7S-30
J=7(10)-30
J=70-30
J=40

Hence their present ages are 70 and 10 :)
if you're not clear about anything, do let me know :)