Hello Sneha and welcome to the Tableau Communities!
Please search in the Forums if you have not already: you should find a lot of people who have asked similar questions.
If you can't find exactly what you need, I recommend you post this in Forums, rather than Viz: Viz is generally for challenges and viz discussions: you'll reach a much wider audience of help at Forums.
Can you attach a sample of your data in a .TWBX?
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Good Luck-- Michael
create a field for Non Serious(<5s) and make the value negative. Then, add negative field of serious visitor.
Add fields in this serious : -
- Non Serious(<5s)
- Serious Visitors
- (Serious Visitors - App Starts)
- App Starts
this will work