Show that you have mastery over the idea behind hypothesis testing by calculating some probabilities and drawing conclusions.


Mateus’s bank issued an advertisement saying that 90, percent of its customers are satisfied with the bank’s services. Since he himself wasn't very satisfied, he suspected the ad is false. He surveyed a random sample of 80 of the bank’s customers, and found that only 80, percent were satisfied.
Let's test the hypothesis that the actual percentage of satisfied customers is 90, percent versus the alternative that the actual percentage is lower than that.
The table below sums up the results of 1000 simulations, each simulating a sample of 80 customers, assuming there are 90, percent satisfied customers.
According to the simulations, what is the probability of getting a sample with 80, percent satisfied customers or less?
  • Your answer should be
  • an integer, like 6
  • an exact decimal, like 0, point, 75
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4
  • a mixed number, like 1, space, 3, slash, 4
  • a percent, like 12, point, 34, percent
Let's agree that if the observed outcome has a probability less than 1, percent under the tested hypothesis, we will reject the hypothesis.
What should we conclude regarding the hypothesis?
Please choose from one of the following options.
Measured percent of satisfied customersFrequency
82, point, 524
87, point, 5181
92, point, 5272
97, point, 527