DAX formula problem

[Gordonik]

Dear excel champions

My problem is to find the DAX formula decribing distribution ratio.
Distribution ratio should be calculated as: (based on data below)

Distribution ratio= avg(Number of Visits Where product is available in ALFA stores / Number of Visits where product should be available in ALFA stores , Number of Visits Where product is available in BETA stores / Number of Visits where product should be available in BETA stores) = avg(4/8,3/4) = 62.5%

The fact which complicate this calculation is ALFA stores visited more than once.

I tried everything and could not find the solution.
I hope someone manage to help me with this task

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Table. 1
ALFA	aaa	02.12.2013
ALFA	bbb	02.12.2013
ALFA	ccc	02.12.2013
ALFA	ddd	02.12.2013
ALFA	aaa	15.12.2013
ALFA	bbb	15.12.2013
ALFA	ccc	15.12.2013
ALFA	ddd	15.12.2013
BETA	aaa	16.12.2013
BETA	bbb	16.12.2013
BETA	ccc	16.12.2013
BETA	ddd	16.12.2013

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[TD="class: xl65, width: 64"]Client[/TD]
[TD="class: xl65, width: 81"]Product ID[/TD]
[TD="class: xl65, width: 92"]Visit date[/TD]
[TD="class: xl65, width: 198"]Number of Visits where product should be available[/TD]
[TD="class: xl65, width: 196"]Number of Visits Where product is available[/TD]

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[Gordonik]

Anyone helps? What function should I use: calculate, average, averagex, summarize, filter, count, countx, earlier, sumx, discount, countrows?
I do not know which ones are appropriate and how to join them in a one formula/measure.

thx for any posts