The pair of equations $x-2y=8$ and $5x-10y=10$ is:

a₁/a₂ = 1/5 and b₁/b₂ = −2/−10 = 1/5, but c₁/c₂ = 8/10 = 4/5. Since the coefficient ratios are equal but differ from the constant ratio, the lines are parallel and the pair is inconsistent.