TOPIC: Discount applied for registering for multiple events

I wanted to know if you can somehow add a discount for a certain event when someone registers for another event that is tagged to this event.

I do not want to use the username and password feature.

Example:

Joe Registers for ABC Event, and when registering their is an add-on event "XYZ Event" at the bottom, so if they check a box, it applies a discount for that event and simultaneously registers them for the XYZ event also.

Thanks