A school teacher is worried that the concentration of dangerous, cancer-causing

Question

A school teacher is worried that the concentration of dangerous, cancer-causing radon gas in her classroom is greater than the safe level of 4pCi/L. The school samples the air for 36 days and finds an average concentration of 4.4pCi/L with a standard deviation of 1pCi/L.

Refer to Exhibit 9-4. At a 5% significance level, the decision is to ___________.

reject we can conclude that the mean concentration of radon gas is greater than the safe level

reject we cannot conclude that the mean concentration of radon gas is greater than the safe level

do not reject we can conclude that the mean concentration of radon gas is greater than the safe level

do not reject we cannot conclude that the mean concentration of radon gas is greater than the safe level

Explanation / Answer

The 1st option is right. In detail answer below:

Ho : Mu < 4
Ha: Mu >=4

n = 36, Sample mean = 4.4, std error = stdev/sqrt(n) = 1/sqsrt(36) = 1/6

Z = (4.4-4)/(1/6) = 2.4

Since, Z of 2.4 has a p-value = 1-.9918 = .0182 which is less than .05 we have the fact that we have to reject Null hypothesis to conclude that Ha is right

Option A is right

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