Every year, the veterinary hospital at a major research university treats a number of horses that have stones called enteroliths in their guts. A sample of 20 years shows that on average about 2% of horses presenting at the veterinary hospital are treated for enteroliths. Some breeds of horses seem more prone to developing enteroliths than others. Below is a table with the distribution of enteroliths among the breeds. The probability that a horse arriving at the veterinary hospital is not an Arabian or a quarter horse is:
A)0.55.
B)0.25.
C)0.45.
D)0.75.

Question

Every year, the veterinary hospital at a major research university treats a number of horses that have stones called enteroliths in their guts. A sample of 20 years shows that on average about 2% of horses presenting at the veterinary hospital are treated for enteroliths. Some breeds of horses seem more prone to developing enteroliths than others. Below is a table with the distribution of enteroliths among the breeds.  The probability that a horse arriving at the veterinary hospital is not an Arabian or a quarter horse is:
A)0.55. 
B)0.25. 
C)0.45. 
D)0.75.

Quizplus · Accepted Answer

From the table, we see that the percentage of Arabians and quarter horses with enteroliths is 3.2% and 3.4% respectively. Therefore, the percentage of horses that are not Arabians or quarter horses with enteroliths is 2% - 3.2% - 3.4% = -4.6%. Since this percentage is negative, it doesn't make sense to talk about it as a probability. However, the percentage of horses that are either Arabians or quarter horses with enteroliths is 3.2% + 3.4% = 6.6%. Therefore, the probability that a horse arriving at the veterinary hospital is not an Arabian or a quarter horse is 1 - 0.066 = 0.934, or approximately 0.45.

Every Year, the Veterinary Hospital at a Major Research University