# Variable change when user upates an answer?

I'm trying to build a course to help our users count money. I've done all the coding and all the math so everything works EXCEPT if they make a mistake and change a number to correct it. Then it adds the number a second time. What do I need to add so they can correct an answer but not clear everything out?

I haven't added the wrong answer part yet, but figured out how to do that. I found they had to reset the whole thing to clear it and start over, otherwise it kept adding the new numbers in.

As you've discovered, you have to be very careful about when you perform math operations on a number variable.

There's a simple solution to your problem: reset the Total, and then add all of the variables every time the user edits one of the "How many..." fields.

And a simple way to do that: Every time one of those variables changes, show a "counting" layer. Don't put any objects on that layer. Just do the math, and close it.

This is shown in an edited version of your slide in the attached file.

FYI: Here's more info about using invisible layers: TIP: the Incredible Power of Invisible Layers | Articulate - Community