An article reported that patients under care for HIV have CD4 tests every 4 months on average with a standard deviation of 1.5 months. What is the probability that in a sample of 60 patients, the mean time between tests exceeds 4.5 months?
Solution :
Given that ,
mean = = 4
standard deviation = = 1.5
n = 60
= 4
= / n = 1.5 / 60 = 0.19365
P( >4.5 ) = 1 - P( <4.5 )
= 1 - P[( - ) / < (4.5-4) / 0.19365]
= 1 - P(z <2.58 )
Using z table
= 1 - 0.9951
= 0.0049
probability= 0.0049
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