Discount - by: okkhalid

Hello,
I would like to smooth the registration to events, we have 5 discounts codes for different people

Regular People - no discount code
University students [discount code with 20%]
College students [discount code with 15%]
seniors [discount code with 10%]
returned customers [discount code with 5%]

How I can make the codes apply automatically when they fill the form of the registration.
So I'm thinking there will be a drop down field that says:
I'm : Select one
New Customer
University Student
College Student
Senior
Returned Customer

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please can you help to do this.

Thank you so much

Please help.