kungfusaini
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#1
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Hi guys,

I usually find creating expressions easy, apart from ones like this:

For every 3 rubbers ordered, at most 5 pencils should be ordered, where x is the number of rubbers and y is the number of pencils.

I always seem to get the expression the wrong way around, could anyone shed some insight into this topic? Thanks!!
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mqb2766
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A very simple, naive
y/5 <= x/3
which is a linear inequality. Not necessarily represents, the integer trunction part of the problem, if there is one. Its just ratios.
(Original post by kungfusaini)
Hi guys,

I usually find creating expressions easy, apart from ones like this:

For every 3 rubbers ordered, at most 5 pencils should be ordered, where x is the number of rubbers and y is the number of pencils.

I always seem to get the expression the wrong way around, could anyone shed some insight into this topic? Thanks!!
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kungfusaini
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(Original post by mqb2766)
A very simple, naive
y/5 <= x/3
which is a linear inequality. Not necessarily represents, the integer trunction part of the problem, if there is one. Its just ratios.
I got what you did but...
The actual solution to the problem is 5y >= 3x.
I'm still lost, even my teacher said he is unsure haha.
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mqb2766
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According to your logic at the start. If 21 rubbers are ordered, at most 35 pencils should be.
so
y <= 5x/3
Can you explain your solution?

(Original post by kungfusaini)
I got what you did but...
The actual solution to the problem is 5y >= 3x.
I'm still lost, even my teacher said he is unsure haha.
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kungfusaini
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(Original post by mqb2766)
According to your logic at the start. If 21 rubbers are ordered, at most 35 pencils should be.
so
y <= 5x/3
Can you explain your solution?
Name:  Capture.JPG
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This is the question, where Y is the number of fruit scones and X is the number of plain scones
Name:  Capture1.JPG
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Size:  1.0 KB
This is the solution.
I agree what you said seems correct, but this is what is written in the Mark Scheme2
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mqb2766
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you've switched the meaning of x and y compared to the original post.
(Original post by kungfusaini)
Name:  Capture.JPG
Views: 34
Size:  7.3 KB
This is the question, where Y is the number of fruit scones and X is the number of plain scones
Name:  Capture1.JPG
Views: 33
Size:  1.0 KB
This is the solution.
I agree what you said seems correct, but this is what is written in the Mark Scheme2
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ghostwalker
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(Original post by kungfusaini)
The actual solution to the problem is 5y >= 3x.
This can't be right as there is no upper limit on the number of pencils (y), whereas the question has "...at most 5 pencils...."

Agree with mqb2766.
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kungfusaini
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(Original post by mqb2766)
you've switched the meaning of x and y compared to the original post.
Bloody hell, I must be going soft in the head. I get what you do now, instead of dividing each variable by its given amount, I was multiplying it!
Thanks ever so much for your help and apologies for the mix up
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