Definite's Extractor

My findings on Life, Linux, Open Source, and so on.

Why some teachers say 5×3 does not mean 5+5+5

A child was marked as incorrect for translating “5×3” to “5+5+5” on a grade school math test.

Further discussion is at http://www.iflscience.com/editors-blog/teacher-marks-child-s-55515-answer-incorrect

According to Common Core: Represent and solve problems involving multiplication and division,  5×3 should be interpret as 5 groups of 3 objects each, which means 3+3+3+3+3.

I think this come from how every-day English express this kind of thing. Like 5 apples (apples appear 5 time), and 5 3’s is similar (3 appears 5 time). This also affect the definition of multiplicand and multiplier. Quote from Wikipedia Multiplication

When thinking of multiplication as repeated addition, the number to be multiplied is called the “multiplicand”, while the number of addends is called the “multiplier”.

In other world, 5×3 should be read as:

3 multiplied by 5

But for division, 5 ÷ 3 is read as:

5 divided by 3

IMHO, this is indeed confusing and inconvenient. If a teacher trying to teach multiplication using the word “multiplied” with blackboard and chalk, she need to

  1. Write 3 first, and say “three”
    Become:  3
  2. Write ×,  and say “multiplied by”
    Become: × 3
  3. Write 5, and say “five”
    Become: 5 × 3

Right to left writing, which is not a usual practice in English.

If the teacher  insists on left to right writing, she has to say “three” when she write “five”. 😛

Luckily, we have times to rescue. 5×3 should be read as:

5 times 3
Advertisements

One response to “Why some teachers say 5×3 does not mean 5+5+5

  1. Damian Jansen 2015/11/04 at 4:39 pm

    This makes my blood boil.
    Yes, in the strict form of “Common Core” maths the forced “left times the groups of the right” means the child did not adhere to the rules and was “incorrect”. But that ridiculous notation makes a mockery of the commutative properties of mathematics and should be outlawed.
    That child will now have had their confidence shaken by the bureaucratic nonsense of US schooling. It’s no wonder they give up and end up struggling for the rest of their school career.

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: