Give the value of $0-1+2-3+4-5+\ldots-49+50$.

Only a numerical answer is expected $i c$.
We group the terms in pairs:

$$
0+(-1+2)+(-3+4)+(-5+6)+\ldots+(-49+50)
$$

Each subtraction inside a parenthesis equals 1, and there are $\frac{50}{2}=25$ such parentheses. Therefore, the sum is 25.

Comment: The vast majority of students found the correct answer, often by providing only the result.