Other people (regular people) pay houses off over the years or write a check
Partial differentiation of a function with more than one variables refers to its derivative being taken with respect to one of those variables, while the rest being held as a constant.
An example is the volume of a cylinder given by:

The volume requires two variables in order to work out the volume, namely the radius and the height.
Using partial differentiation, its partial derivative can become:

This symbol is used in place of the derivative symbol, in order to distinguish total derivatives and partial derivatives.
They would be 10 and 1/2
Multiplying by 1/2 is basically dividing by 2, so 10 times 1/2 would be 10 divided by 2, which is 5
10 + 1/2 is also 10 1/2


Hope you could understand.
If you have any query, feel free to ask.