adding selected numbers together

I am worki开发者_运维知识库ng on a project that needs to add selected numbers together and show answer. so if I have say 10 textfields with numbers and the user picks three of them I want to show that total.

thank you

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The first question is how does the user "pick" the text fields?

After that it's simply writing a method that uses the same selection criteria to add the values.