WGU Updated Applied-Probability-and-Statistics Exam Questions and Answers by jorgie

The probabilities of all possible outcomes in a sample space must sum to 1. In this experiment, the bag contains only red, blue, and green balls, so these three outcomes exhaust the sample space. The probability of drawing a red ball is 0.3, and the probability of drawing a blue ball is 0.6. Their combined probability is 0.3 + 0.6 = 0.9. The remaining probability must belong to drawing a green ball. Therefore, P(green) = 1 − 0.9 = 0.1. This can also be viewed as a complement problem: green is the complement of drawing either red or blue when those are the only other colors available. Option B repeats the red probability, option C would make the total probability exceed 1, and option D is the combined probability of red or blue rather than green. References/topics from the Study Guide: probability sum rule, complements, sample space, mutually exclusive outcomes.

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Simpson’s paradox occurs when an association observed in aggregated data reverses or conflicts with the association observed within relevant subgroups. In this case, the overall recovery rate appears better for Treatment Y, since Y has a 90% overall recovery rate compared with 80% for Treatment X. However, after the data are divided by age group, Treatment X has a higher recovery rate in every age group. That reversal between the overall comparison and the subgroup comparisons is precisely the defining structure of Simpson’s paradox. Age group functions as the lurking or confounding variable because different age distributions across treatment groups can distort the overall recovery rates. Option B states a true overall fact, but it ignores the contradiction created by the age-specific rates. Option C is too general; simple differences between treatments do not necessarily create Simpson’s paradox. The key issue is inconsistency between aggregate and stratified results. References/topics from the Study Guide: two-variable data, confounding variables, conditional comparisons, Simpson’s paradox.

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A 95% confidence interval provides a plausible range of values for an unknown population mean based on sample data. The interval (45, 55) means the method used to construct the interval captures the true population mean in approximately 95% of repeated samples under the same conditions. In practical exam language, the correct interpretation is that the population mean is estimated to lie within the interval with 95% confidence. Option B states the midpoint of the interval, 50, but the question asks for the correct confidence interval interpretation, not just the center. Option C is incorrect because the population mean is not always the upper endpoint. Option D is imprecise because once an interval is computed, it is fixed; the confidence level refers to the long-run success rate of the procedure, not a changing probability attached to that exact fixed interval. Study Guide references/topics: confidence intervals, population mean, point estimate, margin of error.

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In a standard deck of playing cards, every card is either red or black. Red cards consist of hearts and diamonds, and black cards consist of clubs and spades. There are 26 red cards and 26 black cards, for a total of 52 cards. The event “red or black” includes all possible cards in the deck. Therefore, the probability is 52 favorable outcomes out of 52 total outcomes, which equals 1. A probability of 1 means the event is certain. Option B, 1/2, would be the probability of drawing a red card alone or a black card alone, not red or black. Option C would mean the event is impossible, which is false. Option D would correspond to one suit out of four, such as hearts only. The word “or” combines both color categories, covering the entire sample space. Study Guide references/topics: sample space, certainty, addition rule, card probability.

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