Równość 1/4+ 1/5+ 1/a=1 jest prawdziwa dla

$\displaystyle a =\frac{11}{20}$\displaystyle a =\frac{11}{20}

$\displaystyle a =\frac{8}{9}$\displaystyle a =\frac{8}{9}

$\displaystyle a =\frac{9}{8}$\displaystyle a =\frac{9}{8}

$\displaystyle a =\frac{20}{11}$\displaystyle a =\frac{20}{11}