Question 905849


given:

the sum of two numbers, {{{x}}} and {{{y}}}, is {{{80}}}:
{{{x+y=80}}} ..............eq.1

 and their difference is half their addition:

{{{x-y=80/2}}}

{{{x-y=40}}}.............eq.2

solve the system:

{{{x+y=80}}} ..............eq.1
{{{x-y=40}}}.............eq.2
_______________________________add both

{{{x+y+x-y=80+40}}}

{{{2x+cross(y)-cross(y)=120}}}

{{{2x=120}}}

{{{x=120/2}}}

{{{highlight(x=60)}}}

find {{{y}}}

{{{y=80-x}}} 
{{{y=80-60}}}
{{{highlight(y=20)}}}