$\left( \frac{1}{4.9}+\frac{1}{9.14}+\frac{1}{14.19}+...+\frac{1}{44.49} \right)\frac{1-3-5-7-...-47-49}{89}-\frac{19}{28}$

= $\frac{1}{5}\left( \frac{1}{4}-\frac{1}{9}+\frac{1}{9}-\frac{1}{14}+\frac{1}{14}-\frac{1}{19}+...+\frac{1}{44}-\frac{1}{49} \right).\frac{1-(3+5+...+47+49)}{89}-\frac{19}{28}$

= $\frac{1}{5}\left( \frac{1}{4}-\frac{1}{49} \right).\frac{1-(3+49).24:2}{89}-\frac{19}{28}$

= $\frac{1}{5}\frac{45}{196}.(-7)-\frac{19}{28}$

= -1

Vậy giá trị của biểu thức Q là: -1