A little confusion with the Knapsack problem (a worked example)
The (non-negative) variables $x_1,x_2,x_3,x_4$ must satisfy the constraint
$$ 2x_1+2x_2+4x_3+5x_4 \leq 8. $$
If $x_1=x_2=1$ then this simplifies to
$$ 4x_3+5x_4 \leq 4, $$
which implies in particular that $x_3 \leq 1$ and $x_4 \leq 4/5$ (since $x_3,x_4 \geq 0$).