Maths: this does not make sense!

[theweekendisnear]

Hello,

Could you please explain this question to me? How would you answer it?

I'll give you my point of view later, after I listen to yours...

The question is:
"How many times can you double 14 before you go over 100?"

Thanks for any help you can give!

hmm#
I'd argue you can only double 14 once
I know what it means, not sure how it should be worded

I would say double 14 get you 28, double it again and you get 56, so twice. If you double it for a third time you are at 112 so over 100. My answer would be two but it's not a very clearly written question.

In normal speech though, the 'it' in your second sentence would refer to the '14' in your first sentence. But you're no longer doubling 14, you're doubling 28.

I agree that you can double 14 only once - giving answer 28.

But if it means: start with 14 and keep doubling, then it produces a sequence: 14, 28, 56, 112 - giving answer 56.

I would say double 14 get you 28, double it again and you get 56, so twice. If you double it for a third time you are at 112 so over 100. My answer would be two but it's not a very clearly written question.

Sorry - don't know why that posted twice

OK you are being a bit literal the weekendisnear - I get same answer as MLP

This is an exercise in asking a student to double and to track the result of the various doublings until s/he surpasses 100

START - 14
Double 1 - 28
Double 2 - 56
Double 3 - 112

Therefore 3 'doubles' puts you over 100 - so you can only double twice before going over 100.

HTH

Can I just clarify, I know how it should be worded in mathematical terms :o

But, pastsellbydate, "literally" is what Maths is all about... If there is space for interpretation, it's not Maths anymore.

To complicate things even more... The answer "1" to the question
"how many times can you double 26 before you reach 100" was apparently wrong...

I am sooo confused...

Hi theweekendisnear

I take your point - math is meant to be literal and understandable - but only in equation form. The issue here is the teacher/ workbook/ website has poorly expressed what they're saying (and maybe you're being a bit of a stickler for precision in directions).

So take the number 14

Double it - you get 28 (are you with me here?)

Then (IGNORE THE DOUBLE 14 instruction - but think and if I double that product (effectively 2 x 14 = 28 and then double the 28) what do I get)

Doubling 28 gives you 56

and if you double that product (2 x 56)

you get 112 (which exceeds the 100 limit arbitrarily set by teacher/ workbook/website/ etc...)

So how many doubles of 14 (and subsequent products - if that makes more sense) can be performed before exceeding 100

START with 14 (NO DOUBLES YET)

DOUBLE #1 (2 x 14) = 28

DOUBLE # 2 (2 x 28 - 28 being the product of the first doubling) = 56

DOUBLE #3 (2 x 56 - being the product of the second doubling) = 112

112 exceeds 100

therefore you can only double 14 (and subsequent products) 2 times

ANSWER = 2

Was that correct?

Is that clearer?

-------

It's really a principle of doubling, then doubling that product again, then doubling again until you exceed the limit.

An example of the technique would have helped (and maybe you can write a brief note to the teacher saying you found this a bit confusing and perhaps in future providing a worked example first might help).

HTH

Well it would be 2
double it once - 28
double 'it' twice - 56

But I agree with you that maths is meant to be literal. There should be no wiggle room.

But they don't say 14 (and subsequent products)

I think the answer is to send it back and ask for a more formal specification

"How may times can you perform a doubling operation, starting with 14, before the result is greater than 100?"
would be more accurate.

But the doubling 26 question throws that interpretation into doubt, doesn't it?

2 times
14..doubled = 28...doubled =56.

I can see the wording is tricky and not very mathematical.

It is very badly worded!

Reminds me of the time DS was asked to "write the number eighty six backwards" meaning 68 (I think) and he put the answer as "xis ythgie"

I think they wanted to know how many times you can fit 14 (or 26 in the second questions) into 100.

I'll ask DC to find out from the teacher.

Another one that really annoyed me is:
"If a stick is 2.6 m long, and another stick is 2.2 m long, what is the difference in length?"
Answer, marked wrong: 40 cm

DC: "Why is it wrong?"
DT: "Because this test is to test decimals, so the correct answer is 0.4 m"

I think we need Maths specialists in primary schools.

Oh yes I see. I missed the significance of the 26 question.

It is possible they meant to say 'how many times can you multiply 14 before you go over 100'. The question about difference in m is actually fair enough, although not because it was meant to be testing decimals but because you shouldn't mix units in a calculation for that way lies disaster.

Russianonthespree, I disagree about the units question! I think the sensible answer is in cm, not in metres. If, in real life, you asked:
"child A is 1.2 m tall, child B is 1.3 m tall, how much taller is A compared to B?". I would answer 10cm, not 0.1 m
I think the answer in metres kind of lacks a sense of "real world" maths.

weekend it doesn't matter of you disagree, it's a fact that if you don't understand how to work in units you might fall over once you start doing work with volume or area. Now, some kids do understand and can switch. But many can't and thus fall over. Unit discipline is actually important. In the real world. Believe it or not.

I dout the teacher ctually meant double. Bad wording. i suspect she meant how many times can your x 14. Eg 2x14=28 3x14=42 4x14=56 etc so the answer would be 7

how on eaerth would the answer be 7?

Oh I see what you mean
But that isn't doubling

Do you know the "correct" answer to "how many times can you double 26 before you reach 10"?