SSRS: Interactive sorting by Percentage

Scenario:

I wanted to do interactive sorting by percentage but it was not sorting correctly.

It was showing ascending order sorting like:

Null
Null

99.5%

98.4%

97.8%

100%

100%

100%

You can see it was sorting descending order first..........

Solution:

1. Go to table column header textbox(talktime) properties, 
2. Click on "interactive Sorting" 
3. Add sort expression as your required percentage formula:
    "(sum(talktime) / sum(talktime)/sum(holdtime))"
4. Then click ok. 

Even you can add sorting to header "holdtime" text box with respective formula.