Answer:
[-1/2,1/20]
Explanation:
In terms of inequalities, we are asked to find all $u$ such that $2u\ge -1$ and $-20u\ge -1$.
The solution to the first inequality, obtained by dividing both sides by $2$, is $u\ge -\frac{1}{2}$.
We can solve the second inequality by dividing both sides by $-20$, but because we are dividing by a negative number, we must reverse the direction of the inequality: $u\le \frac{1}{20}$.
The set of $u$ which satisfy both inequalities simultaneously is thus $\boxed{\left[-\frac{1}{2},\frac{1}{20}\right]}$.