there are two pieces, both divided in 10 equal segments.
so each piece is 10/10, or namely 1 whole.
two pieces, 10/10 each, is 20/10 for the whole thing, but there are only 11 shaded, so if we take 20 to be the 100%, what is 11 off of it in percentage?
[tex]\bf \begin{array}{ccll} amount&\%\\ \cline{1-2} 20&100\\ 11&x \end{array}\implies \cfrac{20}{11}=\cfrac{100}{x}\implies 20x=1100\\\\\\ x=\cfrac{1100}{20}\implies x=55[/tex]
