pie chart on 70/20/10 ratio based on sales

Experts,

I have a requirement where I have to show pie chart based on sales where I need to show number of customers who contributes towards 70/20/10 % of the total sales. Pie chart Slice should be divided on 70/20/10% of the total sales but the value on each slice should show the number of customer who contributed to that sales. I guess it's similar to Pareto analysis. How do I achieve this in webi?

Thank you in advance

Dar