Question 1204835
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The sum of age's of a man and his daughter is 120years.six years ago,the man's age was thrice that of his daughter.
find their present age.
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The sum of age's of a man and his daughter is T years. v years ago, the man's age was k times that of his daughter.
find their present age.
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Man, y
Daughter,T-y


{{{highlight_green(y-v=k(T-y-v))}}}, with only y, as the unknown variable (the man's age).


{{{y-v=kT-ky-kv}}}

{{{y+ky=v+kT-kv}}}

{{{y(1+k)=v+kT-kv}}}

{{{highlight_green(y=(v+kT-kv)/(k+1))}}}


The description gave 
T=120
v=6
k=3
y is solved; only need to substitute the given values.
{{{y=(6+3*120-3*6)/(3+1)}}}

{{{y=(6+360-18)/4}}}

{{{y=(360-12)/4=90-3}}}

{{{highlight(y=87)}}}-----------the man
{{{T-y=highlight(33)}}}---------daughter