Question 1137545


supplementary angles are two angles whose sum is {{{180}}}°

let one angle be {{{alpha}}} and its supplement {{{beta}}}

 {{{alpha+beta=180}}}°

if one angle is four fifths as large as the other, we have {{{beta=(4/5)alpha}}}

substitute it in  {{{alpha+beta=180}}}°

 {{{alpha+(4/5)alpha=180}}}°......both sides multiply by {{{5}}}

 {{{5alpha+4alpha=180*5}}}°

{{{9alpha=900}}}°

{{{alpha=100}}}°

then {{{beta=(4/5)100}}}°=>{{{beta=80}}}°