VB/ Formula advice needed

Hello, i hope someone can help

Ive got a spreadsheet A1 + B1 = C1 (A1 sources data from other sheets). I want to be able to allow the user to put a "score" in B1 so it changes the total of C1 but then i want the cell to clear but it not affect C1 total ready for the next score to be put in. I would ideally like to be able to do it on a drop down box or something similar but dont know where to start. I hope someone can understand this. Thanks for any help.

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Sorry to be a stickler... but that title is not really any more acceptable...

Try something like:

Clearing cell referenced by a formula but keep result in tact

It should be more descriptive of the topic.