How to change the value of textbox based on another field value?

if i have a field with say a number from 30-49, how can i have another field show "30-49" and so on.  This is being used to determined the age group category for a someone based on their age.  For instance a 28 year old would make the field say "20-29"

Hello rmccoy,

I am not sure if I have understood your question correctly.

Do you mean to say that you want to change the value of a textbox based on the value of another form field?

Yes it is possible to achieve your requirement by taking advantage of our conditions feature. I did check your last edited form and found that you have a form field "AGE CATEGORY". Is this the field where you want to show the range based on the value of "AGE" field? Please check the screenshot below how to achieve this:

You may also like to take a look the following demo form I created for your:  https://form.jotform.com/61287509002956  Feel free to clone this form for a closer look. The following guide should help you in form cloning:  https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL 

Hope this helps.

Do try it out and get back to us if you have any question.

Thank you!