Question 1153528

let your age be {{{x}}}

if your sister is {{{8 }}}years older than you, her age is

{{{x+8}}}

if your combined age is {{{half}}} the age our grandfather who is {{{68}}} years old, than

{{{(x+x+8)=68/2}}} 

{{{(2x+8)=34}}} 

{{{2x=34-8}}} 

{{{2x=26}}} 

{{{x=13}}}->your age

 {{{x+8=13+8=21}}}->your sister's age


check the sum: {{{13+21=34}}} which is {{{1/2}}} of {{{68}}}