Why 5 x 3 = 5 and 5 and 5 Was Marked Wrong • Hacker News Board

Re: Why 5 x 3 = 5 and 5 and 5 Was Marked Wrong

#151

Post by BarryReitman » Mon, Nov 02, 2015, 3:26 AM UTC

Sharlin wrote: post #11

Requiring students to blindly memorize and regurgitate arbitrary definitions and punishing the use of intellect and common sense is the worst possible way to teach math. Or anything else for that matter.

I totally agree, Sharlin. But only because memorization techniques aren't taught. It it were made simple — as it can be! — acquiring facts and data make intellectual considerations much easier and more valuable.

Memory and intellect complement each other.

Barry Reitman Author: "Secrets, Tips, and Tricks of a Powerful Memory." www.PowerfulMemorySecrets.com

Re: Why 5 x 3 = 5 and 5 and 5 Was Marked Wrong

#152

Post by jeremysmyth » Mon, Nov 02, 2015, 11:03 AM UTC

signal11 wrote: post #145

jmilloy wrote: post #131

Earlier quoted context omitted.

Well, maybe you can find a source, but I can only find sources that define multiplication as I have and then mention that multiplication of, say, real numbers, is commutative.

I'd just like to add a point to jasode's excellent point about getting hung up about orthography, which is that please don't define math using English. It's a terrible thing to do -- for example, the en-us 5x3 = 5 times 3 = 3+3+3+3+3 fails for Spanish speakers. For another, English itself is not very "standard" - some variants of British English would actually read 5x3 as "5, 3 times". Math exists outside of human la…

+1 data point: In my anglophone school system we say 5x3 as "5 multiplied by 3", not "5 times 3". These semantics lead children (and me) to think 5 + 5 + 5 instead of 3 + 3 + 3 + 3 + 3.

Re: Why 5 x 3 = 5 and 5 and 5 Was Marked Wrong

#153

Post by jeremysmyth » Mon, Nov 02, 2015, 11:16 AM UTC

adrusi wrote: post #38

5 3 is pronounced "5 times 3", synonymous with "3, 5 times in sequence". So if the problem given had been presented as "5 times 3" I would agree that that means "3+3+3+3+3". However, just becuase 5 3 is pronounced "5 times 3" doesn't mean that it's exactly the same thing. We pronounce it that way because it's convenient, "times" is a one syllable word that we can inject right where the multiplication sign goes, and h…

It's not pronounced that universally either.

I say "5 multiplied by 3", which informs my interpretation of which value is repeated by which. Another commenter uses the phrase "5 into 3".

When you use an less formal (and inherently ambiguous) language (English) to state a condition in a formal language (used to define multiplication), you're gonna have problems of this nature.