physical chemistry - What is this equation for?

I have been given a formula on the topic of alloys and temperature, however am unsure specifically what this equation calculates. The equation is as follows:

$xC_{1} + (1 - x) C_{2} = C_{3}$

I am assuming that the C's will be given (and possibly represent Specific Heat?) - however exactly what is this equation to represent? What does solving for $x$ achieve?

I know that the letters used may vary, however our teacher has provided no more information due to sickness. I have provided all the information I know.