Question 1067558
Let a, b, c be the sides of the triangle, where
a is the longest and c is the shortest.
{{{a+b+c=100}}}
{{{a=2*c}}} and 
{{{b=c+20}}} so
{{{2*c+c+20+c=100}}}
{{{4*c+20=100}}}
{{{4*c=100-20}}}
{{{4*c=80}}}
{{{c=20}}}
{{{b=20+20=40}}}
{{{a=2*20=40}}}