Respuesta :
True mean = mean (or average)+/- Z*SD/sqrt (sample population)
Now,
True mean has to be less than 48.8 years,
Mean (average) = 48.0 years,
SD = 6.0 years, and
Sample size (n) = 9 doctors
Making Z the subject of the formula
Z= (True mean - mean)/(SD/sqrt (n))
Substituting,
Z=(48.8-48.0)/(6.0/sqrt (9)) = 0.4
From Normal distribution probabilities table,
At Z= 0.4, P(x<0.4) = 0.6554 0r 65.54%
Now,
True mean has to be less than 48.8 years,
Mean (average) = 48.0 years,
SD = 6.0 years, and
Sample size (n) = 9 doctors
Making Z the subject of the formula
Z= (True mean - mean)/(SD/sqrt (n))
Substituting,
Z=(48.8-48.0)/(6.0/sqrt (9)) = 0.4
From Normal distribution probabilities table,
At Z= 0.4, P(x<0.4) = 0.6554 0r 65.54%