Final answer:
To decide which number to put in the numerator when calculating a unit rate, you must consider the specific context of the problem, as the relationship between the quantities you are comparing dictates the placement of numbers in the fraction.
Step-by-step explanation:
When calculating a unit rate, whether a number should be placed in the numerator or the denominator is determined by C) the specific context of the problem. The choice depends on what you are comparing and what unit you want as the result. For example, if you are finding the rate of speed, you would place the distance in the numerator and the time in the denominator to get units of distance per unit of time.
Unit conversions also rely heavily on the context. When converting from one unit to another, you arrange a fraction with equivalent measures, ensuring the unit you want to cancel is placed opposite in the fraction. If you need to cancel out a unit in the numerator, you position that unit in the denominator of the conversion factor, often alongside a '1', which represents the equivalent measure.
An example of using unit rates in a chemical context is when determining a reaction rate or equilibrium constant, where the products of the reaction are placed in the numerator and the reactants in the denominator, as dictated by the balanced chemical equation.