Can you spot why teacher failed primary school pupil for answering 5x3=15 in maths test

Blobbenstein

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When does 5 times 3 not come to 15?

The answer is obviously never but you can understand the confusion for a primary school pupil in the US who got this marked incorrect.

The student's name has been removed from the exam and above the answer the teacher has awarded him a score of -1.

The workings out show that the hapless number cruncher had foolishly worked out the sum total by writing 3 '5's instead of 5 '3's.
How did a primary school pupil fails his maths test for putting 5x3=15?

:potty:
 
... I dont get it
5 + 5 + 5 =15
as is 3 + 3 + 3+ 3 + 3 + 3 which the teacher has marked
the space on the page indicates you only need to write the answer not the working out

anyone get why it's wrong??
 
it was marked wrong because the working out wasn't done in the manner expected, ie three fives rather than five threes.

If that teacher really thought that was wrong, then they should be teaching. But it might have been marking guidelines, which would be even more annoying.
 
If the question is, how much is 5x3 then it should be 5, three times... You are starting out with a 5. Now you're asking to times it by 3. It has to be 5+5+5=15.

If the question is, how much is 3x5, then it should be 3, five times...3+3+3+3+3=15.

That's how it is in Karen's Logical World. [emoji12]
 
That seems overly nit-picky.

But I have to agree with commenters - who would teach that way to multiply to children???

I see that in my own kids - when I was in primary school, we had to learn the multiplication tables by heart, so long, often and quick that it became second nature. Seems that this is not done any more nowadays.

So when I ask my kids (who are 11 and 12 by now) how much is 9x8, I can see them mentally starting to add up 8's in their mind... :mad:
How will they ever check a bill in their head, or make an estimate, if they are lacking the instinctive knowledge that 9x8 equals 72?
 
But ... teaching maths can be a challenge, sometimes...



Teacher: "If I gave you 2 cats and another 2 cats and another 2, how many would you have?"

Johnny: "Seven."

Teacher: "No, listen carefully... If I gave you two cats, and another two cats and another two, how many would you have?"

Johnny: "Seven."

Teacher: "Let me put it to you differently. If I gave you two apples, and another two apples and another two, how many would you have?"

Johnny: "Six."

Teacher: "Good. Now if I gave you two cats, and another two cats and another two, how many would you have?"

Johnny: "Seven!"

Teacher: "Johnny, where in the heck do you get seven from?!"

Johnny: "Because I've already got a cat."
 
No one seems to mention that he also got the next one incorrect by drawing an array of 4 columns of 6 rows instead of 4 rows of 6 columns, even though he got the correct product of 6 x 4 = 24.

Multiplication and addition are commutative and associative. The teacher emphasized using a particular procedure to obtain the outcome based on arbitrary standards of achievement at the expense of an opportunity to reinforce these fundamental concepts. Sad.

I am a math teacher. Trust me, this is getting lots of discussion in academe.
 
@Mr Crunchy , thank you for your input!

So, what is your view on learning multiplying tables by heart?
I must confess that while I have the 10x10 pat down, from the 20x20, I only remember maybe 30 %...

My view is, if you do not "intuitively" know the product of those numbers up to 10x10, how are you ever going to be able to do a division on a piece of paper?
 
I think that is quite unfair!

I remember we had to stand up at the front of the class and the teacher would randomly pick a number and tell you to recite it. I always wanted to get the nine times table as my Dad taught me that the answer adds up to nine so I found it the easiest to learn.:p
 
when I was a kid, I had a little program on my Vic20, with a little maze; and to get from one side to the other you had to pass through random multiplication questions. I think this is a better way to teach the times table. Because it is random, I think you learn the specific coupled numbers, rather than the chanting method.
They could even put a 'learning mode' on computer games, where you have to answer times table questions to progress to the next level.
 
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5 times x is east too....just x times 10 divided by 2.

so 7*5= 70 divided by 2........well I find it easier.
 
Does this mean that you start to calculate when you hear the question "7x5" ? :dizzy:

I don't need to calculate, I immediately know that the result coupled to these numbers is 35, learned that in primary school.
I thought everybody would learn it like that.....
 
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Well I was home educated for a few years..........

helps with higher 5*x numbers anyway. 5*94=470 simple.
 
it is funny though, in my O-Level math exam where we weren't allowed a calculator, I was working out simply multiplications in the margins with a pencil.....I should have spent more time on that Vic20 game.
 
I don't need to calculate, I immediately know that the result coupled to these numbers is 35, learned that in primary school.
I thought everybody would learn it like that.....
Yes, we memorized multiplication of two natural numbers up to 10. I remember most of it, but sometimes have to think a bit.
 
to multiply by 8, just double 3 times eg 13*8=104

same with dividing by 8; halve 3 times


or in binary rotate right 3 times....? :p