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- Thread starter AdkAdi
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Hi Jomo (stupid phone keeps changing yer name to Joni). Had you intended to work with20 <= p/q <=21

20 <= 50p/q <= 21

or are you using a different example for illustration purposes?

In the given exercise, q cannot be 1,2,3,4,6,7,8,9,11,13,14,16,18,19,... because p values would not be Integers.

I'd started by writing

40/100 <= p/q <= 42/100

and thinking about how many p/q would equal 0.4 (i.e., equivalent fractions -- q is multiple of 5), and then I'd wondered if there might be a way to determine how many wouldn't.

(There are no additional fractions equivalent to 21/50, so the only p/q with q=50 would be 20/50 and 21/50.)

Manually checking with low q values, it appeared that the number (n) of p/q without a terminating decimal form appearing after q being a multiple of 5 might be increasing like this:

q, n

5, 0

10, 1

15, 1

20, 2

25, 2

30, 3

35, 3

etc

That would help with counting all p's and q's, but we don't want to include any repeats, so my approach would need a lot of manual checking.

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Hello Adk. What sorts of things has your class been discussing?I have tried transposing the variables

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@Otis is correct, in order to guide you we need to know what strategy your teacher expects you to use. Therefore please show some of your work. In the absence of this, here are a couple of extra ideas...

I'm quite a visual thinker, so personally I'd think about a method to count the number of integer (q, p) grid points in the light blue region of the following graph (including any grid points that lie ON the red lines).

OR, actually, I'd be thinking of writing a computer program to count the solutions since it's such a small set of q values!

I'm quite a visual thinker, so personally I'd think about a method to count the number of integer (q, p) grid points in the light blue region of the following graph (including any grid points that lie ON the red lines).

OR, actually, I'd be thinking of writing a computer program to count the solutions since it's such a small set of q values!

Last edited:

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That would be simplest, but I'm hoping the OP will teach me something from number theory.writing a computer program to count

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Yes, I did mean to write 20 <= 50p/q <= 21Hi Jomo (stupid phone keeps changing yer name to Joni). Had you intended to work with

20 <= 50p/q <= 21

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Computer program sometimes get in the way of real mathematics.@Otis is correct, in order to guide you we need to know what strategy your teacher expects you to use. Therefore please show some of your work. In the absence of this, here are a couple of extra ideas...

I'm quite a visual thinker, so personally I'd think about a method to count the number of integer (q, p) grid points in the light blue region of the following graph (including any grid points that lie ON the red lines).

View attachment 28892

OR, actually, I'd be thinking of writing a computer program to count the solutions since it's such a small set of q values!

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That would be simplest, but I'm hoping the OP will teach me something from number theory.

I know where you're both coming from, and (partly) agree with you both. It does seem very unlikely that @AdkAdi was being asked to write a computer algorithm to solve this. I was trying to illustrate that there are different approaches, and without seeing any work from OP how are we supposed to provide relevant help?Computer program sometimes get in the way of real mathematics.

Last edited:

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Here's an improved image and an extra hint for my first proposed method......I'd think about a method to count the number of integer (q, p) grid points in the light blue region of the following graph (including any grid points that lie ON the red lines).

HINT: Can you see that the number of grid intersection points in 0EAC will be double the number of grid intersection points in 0AC (but you'll need to be careful and take into account the grid intersection points that lie along the outer lines of the shapes).

NOTE: I have not worked this out to an end result, but I think this method could be used to yield a closed form solution for any upper-limit of q (not just 99)

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One way is to ask the OP questions and wait.without seeing any work from OP how are we supposed to provide relevant help?

Another way is to not wait but guess (including a proviso, perhaps).

On the other hand, many replies here are written for a general audience (not concerned with relevance for the OP per se, as long as there's relevance for some students in what they say).

I don't see any issues with your suggestions.