Here is the IB syllabus requirement for this sub-topic:

Monopolistic competition
• Assumptions of the model
• Short-run and long-run equilibrium
• Product differentiation
• Efficiency in monopolistic competition

From www.reffonomics.com a useful introductory slide on calculating price and quantity under monopolistic competition scenario:

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Which then leads to finding profit (from the same site, www.reffonomics.com) :

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One that is earning a loss:

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And one breaking even:

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You can access all the resources here: Microeconomics by Dick Brunelle and Steven Reff – full credit to these industrious authors of the presentations above.

From http://highered.mcgraw-hill.com (McConnell Brue Economics) we have a useful interactive graph to explore with appropriate questions to solve – click on the image or title below

“Explore: How does a monopolistic competitor respond to a decline in demand in the short run and in the long run?”

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Now some video resources:

econsteve12 has given us three parts:

pajholden provides this video: click here

richardmckenzie offers this video:

And finally here is ACDCLeadership’s 60 seconds’ worth: