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Richard
 
The only reliable way is to do what the Dutch do in their A-level and that is to set up a total cost function as a quadratic, and then differentiate it to get Marginal Cost. When you plot this against the AC it will cut at the lowest point.
 
If you don't want to do that , and I wouldn't then you have to interpolate what the value would be on the halves and plot them on the whole. Now there's a challenge for you!
 
But a more important question is whether it is worth time doing this on Excel. It is quicker to plot a quick graph and then get the students on to a case study of Microsoft and a comparison of UK and US antitrust policy!
 
Best of luck
 
Steve
----- Original Message -----
From: [log in to unmask] href="mailto:[log in to unmask]">Richard Young
To: [log in to unmask] href="mailto:[log in to unmask]">[log in to unmask]
Sent: Saturday, October 09, 2004 10:16 AM
Subject: Plotting marginal values in Excel

Thanks to the list I can now plot demand & supply curves in Excel – not bad of a Head of ICT J

 

Ah, but what to do about marginal values eg marginal product and marginal cost

 

With pen and paper you plot half way between what is and what was eg plot the marginal product of the 5th worker half way between 4 and 5 on the x axis where labour is plotted

 

I attach a spreadsheet where I have managed to plot AP & MP but MP does not intersect AP at its highest point because Excel is plotting marginal product at 5 – not 4.5

 

HELP PLEASE – can you get Excel to plot marginal values half way?

 

You may ask why am I bothering – at AS level

 

1. I do like my students to use ICT and nothing like a context

 

2. I have an able class

 

3. I find just drawing curves eg a set short run average cost curves to illustrate economies of scale builds awareness but not understanding. Why is the MC curve shaped like an umbrella?

 

Actually getting into the nitty gritty of diminishing returns gives students the necessary background to understand the short run, diminishing returns for a constant outlay on wages. Never expect to answer a question on deriving curves.  But at least they can get their heads round why so why cost curves are the shape they are.

 

Getting student to work through worked examples is one approach. I am sure there are others.

 

Regards

 

Richard Young

31 Newland Mill

Witney OX28 3HH

 

01993 200110

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