I have this situation and I need help. 

I have requirments to get a number of items with % of grand total : 

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I have an Items with sales. I need to sort sales per item desc. After that i need to calculate % of grand total. (column F) 
After that I need to get Number of ItemNo by % of grand total. 

I need to count number of ItemNo summing % of grand total ( column F ). When I got forexample 50%, i need to count nubmer of items. Forexample summing % from top and after 20 items I got 50% i need to put in 50 % of grand total number of 20 items. After that I need to sum again from top until 75% of grand total, and now i have maybe 37 items.

How i can calculate this? 

thank you

I tried with dax, but unfortunately i cant resolve this. Anybody can help?