Question 653886

let {{{x}}} be sister's age 

if sister is {{{9}}} years older than i am,then I am

{{{x-9}}} 


if the sum of our ages is {{{51}}} we will have:

{{{x+(x-9)=51}}}...solve for {{{x}}}

{{{x+x-9=51}}}

{{{2x=51+9}}}

{{{2x=60}}}

{{{x=60/2}}}

{{{highlight(x=30)}}}...sister's age 

{{{x-9}}} 

{{{30-9}}} 

{{{highlight(21)}}} ....my age