[tex]2\frac{1}{2}*4 \frac{1}{2}-5\frac{17}{20} :\frac{9}{10} =\frac{3}{2}*\frac{9}{2}-\frac{117}{20}*\frac{10}{9} = \frac{27}{4}-\frac{13}{2} = \frac{27}{4}-\frac{26}{4} = \frac{1}{4}[/tex]