What is to do when you have to use more than one unknown variable?

We can solve the equation of two unknown variables for one variable in terms of second variable.

Step-by-step explanation:  

We know that, an equation with a variable can be solve easily. But in the case of two unknown variables, we can solve the equation for one variable in terms of second variable. For example:

If we have given an equation with two unknown variable x+y=4, we can solve this equation for variable y in terms of variable x or we can solve this equation for x in terms of y. Which could be written as:  

y=4-x

or

x=4-y.

question: how many people can she serve?

answer: she can serve 16.66666667 people. so she can only give 16 people a complete serving.

question: does she have enough ice cream for her guests?

answer: no. explanation: she only has enough for 16 people to have a full serving. however, she can give a 17th person a partial serving.