How to filter a table based on a column's highest value

Thanks Anonymous  and Greg  for your solutions. My description of the issue is probably not accurate enough. What I am looking for is not retrieving the minimum quantity for each quantity. I want to retrieve the quantity for the Maximum value in "Period".

So for Quality "A", I want to retrieve the quantity where the value "Period" is the highest, so 10, not 13.

Then I would like to do the same for the minimum Period (so retrieve Quantity 5 for Quality A in Anonymous 's example).

In the end, I would divide the Quantity for the highest Period by the Quantity for the lowest Period, for each Quality. That would give me an index, which is the scope of all the above.

I thought that DAX was the right language to solve this question but I didn't figure out how, despite may trials.

Thanks again for your help!