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really easy? Or hard?

Ok this is one of the question that my 9 year old was asked to do for his homework.

9 x 3 = (4 x 3) + (blank x 3) = blank

The only way i can see that this question works is if the answer to the question is the blank in the brackets so it works out to.

I worked the answer out to 5.

9 x 3 = (4 x 3) + (blank x 3) = blank
27........12

27-12 = 15. So 15 / 3 is 5. The answer to the blank is 5

Is there something im missing?

I left school a good while ago.

Im trying to help the lad solve this question (he just seems to be guessing the numbers) - but he hasnt brought home any of his reference books or shows any way of working it out (and cant explain how to work it out either)

(edited 9 years ago)

Reply 1

xx_Dan_xx

Original post by silverbolt

Ok this is one of the question that my 9 year old was asked to do for his homework.

9 x 3 = (4 x 3) + (blank x 3) = blank

The only way i can see that this question works is if the answer to the question is the blank in the brackets so it works out to.

I worked the answer out to 5.

9 x 3 = (4 x 3) + (blank x 3) = blank
27 12

27-12 = 15. So 15 / 3 is 5. The answer to the blank is 5

Is there something im missing?

I left school a good while ago.

Im trying to help the lad solve this question (he just seems to be guessing the numbers)

That second =blank shouldn't be there.

It should be:

9 x 3 = (4x3) + (x * 3)
As you said;

27 = 12 + 3x
27-12 = 3x
3x = 15
x = 5

You are right.

Reply 2

AranAlpaca

If I were to work that problem with a nine year old, I would approach 9x3 to mean 9 groups of three. The original equation can be thought of as 9 groups of three = 4 groups of three + ___ groups of three. It doesn't matter if one is adding apples, elephants or groups of three. 9 things will always be the same as 4 things + 5 things.

Reply 3

silverbolt

Original post by xx_Dan_xx

That second =blank shouldn't be there.

It should be:

9 x 3 = (4x3) + (x * 3)
As you said;

27 = 12 + 3x
27-12 = 3x
3x = 15
x = 5

You are right.

Its how the question is written out in the work book.

Brilliant thanks, at least i can still figure out this much maths lol

Reply 4

DFranklin

Original post by xx_Dan_xx

That second =blank shouldn't be there.Or it should be there, but there is not supposed to be any implication that both 'blank's contain the same value.

i.e.

9 x 3 = (4 x 3) + (5 * 3) = 27

FWIW, my child is 7, I have a degree and masters in maths, and there are questions in her maths homework where I'm left thinking "I don't know what the answer to this is supposed to be"! (And many, many more where I'm left thinking "I have no idea how a 7 year old is supposed to do this).

Reply 5

xx_Dan_xx

Original post by DFranklin

Or it should be there, but there is not supposed to be any implication that both 'blank's contain the same value.

i.e.

9 x 3 = (4 x 3) + (5 * 3) = 27

FWIW, my child is 7, I have a degree and masters in maths, and there are questions in her maths homework where I'm left thinking "I don't know what the answer to this is supposed to be"! (And many, many more where I'm left thinking "I have no idea how a 7 year old is supposed to do this).

It shouldn't be there. Ok its not wrong as the = blank means is the same value as 9x3. It has to be the same value as 9x3 so its not needed and no-one writes an equation with two equals.

Its most likely an error.

(edited 9 years ago)

Reply 6

DFranklin

Original post by xx_Dan_xx

It shouldn't be there. Ok its not wrong as the = blank means is the same value as 9x3. It has to be the same value as 9x3 so its not needed and no-one writes an equation with two equals.Nonsense, people write things like that all the time. If you look through step solutions I've posted where you end up needing to do arithmetic you'll see me do it often:

E.g. I might write something like: 83 + 17 + 29 + 71 + 49 = 100 + 100 + 49 = 249.

For more advanced mathematics (integration involving integration by parts) it would be unusual NOT to see multiple equal signs in one equation.

(edited 9 years ago)

Reply 7

xx_Dan_xx

Original post by DFranklin

Nonsense, people write things like that all the time. If you look through step solutions I've posted where you end up needing to do arithmetic you'll see me do it often:

E.g. I might write something like: 83 + 17 + 29 + 71 + 49 = 100 + 100 + 49 = 249.

For more advanced mathematics (integration involving integration by parts) it would be unusual NOT to see multiple equal signs in one equation.

That example is completely different to the question asked. You're working through the first sum and making it easier to work out. You're working through an equation which is different as you're finding a variable rather than the overall sum.

Secondly, the intergration by parts is the same instance with your example.

Lastly, this is a 9 year old, he is not doing advanced maths and it would just confuse them to write it as the original post suggests. We both know the =blank is completely uneeded and irrelevant for the question.

Reply 8

DFranklin

You're the one who said "no-one writes an equation like that" (emphasis mine), which is patently not true.

Having seen what my child gets asked at 7, it wouldn't surprise me at all for them to get a question like this in the next year or so.

Reply 9

ThatPerson

Original post by silverbolt

Its how the question is written out in the work book.

Brilliant thanks, at least i can still figure out this much maths lol

I think the second blank is there so they can write the answer to 9x3, so in effect the question tests two things: Solving a simple equation and multiplication.

Reply 10

xx_Dan_xx

Original post by DFranklin

Chill out dude no need to dissect my every word. What you're talking about is writing things like:

9 x 3 = (BLANK + 3)
27 = X + 3
24 = X

Most people use a new line rather than continuing across a page. What I am talking about is the question being like that that is stated in the original post, the question shouldnt be written like that.

Reply 11

davros

Original post by xx_Dan_xx

I have no idea what 9 year olds are supposed to know or whether they're exposed to formal algebra or not at that age, but I think people are taking this question a bit too literally.

If the original question used an algebraic symbol like x in two places instead of the blank, implying that x had the same valiue then I'd agree that the question was wrong because it would be insoluble.

However, if this question is set for people who haven't covered algebra yet and just leaves a blank space for the students to fill in the missing number in each case (which need not - and won't be - the same number) then I can't see a problem with it :smile:

Reply 12

atsruser

Original post by davros

However, if this question is set for people who haven't covered algebra yet and just leaves a blank space for the students to fill in the missing number in each case (which need not - and won't be - the same number) then I can't see a problem with it :smile:

I agree. The blanks are not meant to represent variables. I've seen lots of questions like this in "help your kids with their maths" workbooks.

Reply 13

atsruser

Original post by xx_Dan_xx

You're confusing two very different things. The original question is not supposed to be a set of steps in the solution of an equation, as you have written above: it is a single mathematical statement, just like