Solve the system of equations x + 2y = 10 and 3x − y = 5, then calculate 2x - 2y.

$$3(10 - 2y) - y = 5$$ $$30 - 6y - y = 5$$ $$30 - 7y = 5$$

$$30 - 5 = 7y$$ $$25 = 7y$$ $$y = \frac{25}{7}$$

$$x = 10 - 2\left(\frac{25}{7}\right)$$ $$x = 10 - \frac{50}{7}$$

To combine, find a common denominator:

$$x = \frac{70}{7} - \frac{50}{7}$$ $$x = \frac{20}{7}$$

$$2x - 2y = 2\left(\frac{20}{7}\right) - 2\left(\frac{25}{7}\right)$$ $$2x - 2y = \frac{40}{7} - \frac{50}{7}$$ $$2x - 2y = \frac{40 - 50}{7}$$ $$2x - 2y = \frac{-10}{7}$$

As a decimal, $\frac{-10}{7} \approx -1.42857...$
Rounding to two decimal places, the value is $-1.43$.

Your final answer of $-1.42$ is very close, but due to rounding $y$ to 3.57 and $x$ to 2.86 in intermediate steps, there's a slight difference.

The more accurate value is $\boxed{-\frac{10}{7}}$ or approximately $\boxed{-1.43}$.