Thanks Mr. Pimp. Your breakdown of the scenario into numbers helped a lot...however, I'm still bothered by this one thing, so I'd appreciate it if you can help clarify. The new mass compared to the one old is understandable since the new finding showed that the material reflects 60 times less light per unit of mass. However, the premises didn't give enough warrant to assume that the brightness (6000 candelas - using your example) in total would be the same as before. Furthermore, where did they even get the measurement of brightness if they didn't even get the brightness per unit of mass right? I know I'm reading too much into the question...but it's a type of Must Be True question that doesn't feel Must Be True lol
Re-read the stimulus.
Your assumption that the amount of light being reflected has changed is unwarranted. The stimulus say only that the measured reflective properties of the rock have been corrected
. There is no mention that the amount of light being reflected has changed or that the size of the comet has changed. It's still the same comet and it's still as bright as before.
The scientists took a measurement of the amount of light that was reflected, and by using the old reflective properties of the rock
, they were able to determine a mass.
Later, based on new satellite data, scientists determined that the comet is not as good at reflecting light as they previously thought. They did the same calculations with the same data, but this time they used the corrected reflective properties of the rock
to determine a new mass.
Hence, the calculated mass changed because of the corrections in the reflective properties.