# Decision Linear Programming

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#1
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!!
0
2 years ago
#2
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!!
0
#3
(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.
0
2 years ago
#4
According to your logic at the start. If 21 rubbers are ordered, at most 35 pencils should be.
so
y <= 5x/3

(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.
0
#5
(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

This is the question, where Y is the number of fruit scones and X is the number of plain scones

This is the solution.
I agree what you said seems correct, but this is what is written in the Mark Scheme2
0
2 years ago
#6
you've switched the meaning of x and y compared to the original post.
(Original post by kungfusaini)

This is the question, where Y is the number of fruit scones and X is the number of plain scones

This is the solution.
I agree what you said seems correct, but this is what is written in the Mark Scheme2
0
2 years ago
#7
(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.
1
#8
(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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