Is it also correct if I answer $60\times 250$ as the estimation for $57\times 246$?

Question

In a textbook I use for teaching, I found the following.

Question

Why are there only two possibilities? Is it also correct if I answer $60\times 250$ as the estimation for $57\times 246$?

Answer 1

It's working noting that your estimate (15000) is better than theirs since the actual product is 14022 even though you would go into it knowing that it was an overestimate.

As a high school math teacher, I've never heard of a strategy for teaching estimation as being wrong. At worst, your students will miss one question on a bogus standardized test. If you can train them to quickly estimate what an answer will be before they calculate it so that they can actually strive to understand the results of their work, that is a really really small price to pay.

Answer 2

The authors did not claim there were only two possibilities. They simply listed two as examples and (presumably) left the rest for anyone to come up with. Indeed, they couldn't have listed all possibilities if they'd wanted to as there are infinitely many.