sometimes i still don’t know how to do these types of problems

Question

A scientist wants to determine if a type of yeast will make a cake rise. The 

scientist bakes one cake with the yeast and one cake without the yeast. Which of the following is the variable in this experiment?

Answer 1

The variable in this case is the yeast. The control is the cake without the yeast. The scientist knows the behavior of the cake without the yeast added, so presuming that the scientist bakes two cakes in the same oven at the same temperature after letting both sit out for the same amount of time, and the only difference is that one has the yeast and one does not, your variable is the yeast, your hypothesis is "I think this yeast will make the cake rise", your conclusion is drawn from whether or not the yeast does in fact make the cake rise.