Record text input in excel

Hello everybody! This is what I'm trying to do.

I'm recording an excel simulation, but I want my test takers to type in on their own a formula in one of the cells. The simulation is OK in terms of letting my students choose the right buttons and options, but it also records when I type in the formula, and that's what students have to do on their own. Sorry if this a very rookie question. Please, help! Thanks!