You are overlooking the fact that the teacher is marking the methodology, not the result.

The point being made by the teacher is that the student wasted a lot of time doing it his way.

By recognizing that you could turn the subtraction into easier numbers by adding the same amount to both sides, the student could shorten the time taken to reach a correct answer. As demonstrated by the laborious nature of the workings shown, as opposed to the simplicity of the mental processes advocated.

>>I hope that teacher gets a job in a bank, I will go in and ask for a friendly $290 so that person will really give me $300.<<

But that would not happen. It is not the answer that is "friendly", it is the methodology.

Storm. Meet teacup.

its hardly a storm in a tea cup
its more like INSIDER TRADING
[I LIKE TO THINK IM OVER SECOND GRADE MATH
BUT EVEN I COULDN'T MAKE SENSE OF IT..SIMPLY BY LOGIC*

thus its a spin..that cant be reasoned out..to catch not the dumb..but those kept deliberately ignorant[by this simple trICK..YOU CAN GET A WRONG SCORE FOR THE RIGHT ANSWER/SIMPLY BECAUSE FRIENDLY NUMBERS ALLOw collusion/BY Unfriendly means

daddy..what is a friendly number?
is iT A WHOLE NUmber a positive number or a negaTIVE NUMBER

FRIENDLY MEANS YOUR CLEVER AND YOUR NOT..
NOT CAUSE YOU DONT KNOW THE CORRECT/Number/..but cause you mistook a word..yet its not friendly..its a trick

why REUSE OLD WORDS..WHOS MEANING IS CLEAR
TO COME IP WITH NEW TRICKS..TO MAKE SOME LOOK DUMB
WHY NOT CALL IT THE PERICULES ADJUSTMENT..OR THE ROUNDING SIMPLIFICATION

ITS INVENTED to seem too DAMM CLEVER
AND FURTHER CONfound thOSE.NOT IN THE KNOW

OUG, I agree with Pericles and you....as P said, this particular exercise is about the methodology.....but in saying that I live with secondary teachers and they complain that the kids coming up from primary are lacking in basic math and comprehension. The secondary teachers blame the pre secondary syllabus, and they would be right. I agree that confusing the issue with “friendly” numbers is a step too far for this age group.

I believe the syllabus was manufactured over the past 30 years by imbecile academics with nothing better to do than fix something that was not broken. It’s like Parkinson’s Law of social workers...the number of clients grow in volume to meet the number of social workers available to deal with them. More non productive academics, more ridiculous and useless academic tangents added to our scholarly lives.

Before the non productive tangent engineering of our syllabus we had twice the number of kids doing higher mathematics based courses at uni than we do now.....and our population has grown by 30% over that period.

Gee, I think I was only doing simple 1+1 =2 stuff back in grade two. How the world has changed.

Technically the question should have been Something like this.
(530 +30) - (270+30) =

In any case the kid most likely used a calculator which is what most kids do these days.

Besides, I would be more concerned about the school teacher writing skills, as the writing in green is hardly what I would describe as of school teacher quality.

What a pile of garbage. Perhaps this is designed for teachers who can't do mental arithmetic.

Personally, being somewhat dyslexic, I always have a chance of thinking 23, but writing down 32. Every extra step gives me just one more chance to make such a mistake. It is almost designed to cause transposing errors. Many have developed techniques to overcome these difficulties. Doing the calculation in my head, or using a slide rule is for me, much safer than working on paper or with a calculator.

When I was sailing about the ocean, in the days before mere mortals could afford sat nav, I had to do all my navigation the old long way, using sights, tables, & simple calculations. I had to develop a technique to avoid transposition errors putting me on a reef somewhere.

Checking your work is useless, as you will continue making the same mistake, or simply not see it. I used to do the sight twice, using a different assumed position for each. The calculations were different, thus avoiding making the same mistake again, but must give the same position line if done correctly, a positive check that both calculations were right.

Having an education system, or dogmatic teacher, demanding you do it her way would be a real problem for people like me, & the 10s of thousands who have a bigger problem than I have.

I have had some brilliant teachers, some tried very hard, but none of them could ever help with this problem, only hinder.

On the bright side the student has had the chance to learn to carefully read the instructions and/or the question in future...

"1. Draw and label a tape diagram to show how to simplify the problem. Write the new number sentence and then subtract."

Given the student failed to show how to simplify the problem but repeated the simplification of 'adding 10' as exampled in (a) by 'adding 10' to (b) through (e) the teacher's comments were polite.

And I had a giggle that the sidebar advertisement when I followed the link was a picture of a gas-masked, hooded, gun-wielding figure titled "Survive Anything"... though it was a trackthrough to PatriotSurvivalPlan rather than other second-grader maths techniques.