Originally Posted by MumOfThree
Irena I don't think that Dude is arguing with you on the ways the question could be solved - but that the two parts of your sons answer do not match. Your son says "How many more legos are in the new set?" the answer to HIS sentence must be 10, your son is the one that formed a sentence to which the correct answer is subtraction not addition. Dude's problem is NOT directly with what the teacher asked, or the teacher's understanding, but with the internal consistency of your son's answer.

This.

Your son's answer (70 + 10 = 80) does express the relationships, so he clearly understands them. But it does not answer the question at hand. This expression answers a different question that was not asked:

"There are 70 lego pieces in a lego set. A new set comes in the mail with 10 more pieces than the old set. How many legos are in the new set?"

This would be an addition operation, using the two inputs provided, to produce a different solution.

And here's a great example of why it matters:

Originally Posted by Nautigal
Originally Posted by 22B
All this pedantic, rule-based, mechanical procedure for processing "word problems" is something you could program a machine to do. It wouldn't need to understand a thing.

So you're saying, then, that some sort of device, some sort of "calculating" device, could be contrived, in which one could, say, enter numbers and types of operations, and it would somehow extrude the answers?

Such a machine would be hopelessly dumb, so you'd have to walk it through, step by step, every process. If you didn't clearly identify what the inputs are and what to do with the output, as a major IT engineering company often says in its tech notes, results are unpredictable.