Zach works at the Verizon store and wonders if iPhones last longer if the screen brightness is set to low. He selects a random sample of 20 brand new iPhones from this store and
randomly splits them into two groups of 10. For the first group of 10 iPhones, he sets the
screen brightness to low and then starts a movie. For the second group of 10 iPhones, he
sets the screen brightness to high and then starts a movie. For each iPhone, he measures
the amount of time until the battery is all the way dead. He finds that the low brightness
iPhones lasted longer, on average, than the high brightness iPhones.
(a) Was this an observational study or an experiment? Explain your reasoning.

(b) What is the explanatory variable and the response variable?

(c) Was a random sample used to collect the data?
(d) Was random assignment used to set up an experiment?
(e) What conclusion can we make from this study?