You are asked to study the effect of temperature on the volume of a balloon. the balloon's size increases as it is warmed. what is the independent variable? dependent variable? what factor is held constant? how would you construct a control?

Given that there is a study about the effect of temperature on the volume of a balloon. It is found that the balloon's size increases as it is warmed.

So there are two variables "Volume" and "temperature".

Now we have to select between dependent and independent.

Here Volume is dependent on temperature because when you change temperature then volume changes.

Hence independent variable is "temperature".

Dependent variable is "Volume".

Given that as temperature increases (warmed) then volume increases so that means both are in direct proportion and we can write equation

V=kT where V is volume, T is Temperature and k is the constant of proportion.

or we can also write V/T=k

So that means ratio of Volume and Temperature remains constant.

So the required factor which is held constant is "Volume/Temperature"

Control is given by equation V=kT