Suppose that more than a decade ago high levels of lead in the blood put 78% of children at risk. A concerted effort was made to remove lead from the environment. Suppose, according to a survey, only 6% of children in the United States are at risk of high blood-lead levels. In a random sample of 150 children taken more than a decade ago, what is the probability that 105 or more had high blood-lead levels?
A)0.963
B)0.079
C)1.000
D)0.000

Question

Quizplus · Accepted Answer

Given that 78% of children were at risk more than a decade ago, the probability of a child having high blood-lead levels was 0.78. For a sample size of 150, the expected number of children with high blood-lead levels would be 150 * 0.78 = 117. The question asks for the probability of having 105 or more children with high levels, which is essentially asking for a significant portion of the sample to exhibit the common condition of that time. Given the high probability (78%) of a child having high blood-lead levels, it is almost certain (probability = 1.000) that in a sample of 150 children, 105 or more would have had high blood-lead levels, reflecting the widespread issue at the time.

Suppose That More Than a Decade Ago High Levels of Lead