Question

A study found that 25% of car owners in Fiji had their cars washed professionally rather than do it themselves. If 18 carowners are randomly selected, find the probability that atmost two people have their cars washed professionally

Answer 1

13.5%

Explanation:

The probability of interest is the cumulative probability of a binomial probability density function with 18 trials and a probability of success of 0.25. We are interested in the value for x ≤ 2.

Calculator

Such a calculation can be done "by hand" by adding up the probabilities for 0, 1, and 2 people. (A calculator is needed for the arithmetic.) One may as well use the appropriate function of a calculator to find the probability:

binomcdf(18, 0.25, 2) ≈ 0.135

The probability is about 13.5%.