Invite students to share their equivalent expressions and how they reasoned about them. Display their expressions for all to see. Make sure students see that rewriting the expressions as sums or differences involves distributing the division (or applying the distributive property to division). 

If not mentioned in students' explanations, point out that each division could be thought of in terms of multiplication. For example, $\frac {4x-10}{2}$ is equivalent to $\frac12 (4x-10)$, because dividing by a number (in this case, 2) gives the same result as multiplying by the reciprocal of that number (in this case, $\frac12$). Applying the distributive property of multiplication to $\frac12 (4x-10)$ enables us to rewrite this product as a difference.

Expect some students to give $2x-10$ or $4x-5$ as an answer to the first question. To illustrate why these are incorrect, take an example like $\frac{4+6}{2}$. Explain that we know that 10 divided by 2 is 5, but if we divide only the 4 or only the 6 by 2 we won’t get 5. Alternatively, remind students that fraction bars can be interpreted as division, so each expression can be rewritten as, say, $(4x-10) \div 2$, and we can apply the distributive property.

The signs of the numbers in the second expression might be a source of confusion. Students might be unsure if the expression should be $\text - \frac12 -25x$, $\frac12 + 25x$, or another expression. Encourage students to substitute a number into the original expression, then try it in each potential answer. To explain why $\text- \frac12 + 25x$ is correct, appeal to the distributive property again.