Standard Deviation and Mean

Question

In an earlier study men with coronary heart disease has a mean systolic blood pressure of 148 mmHg with a standard deviation of 16.5 mmHg. You wish to repeat this study with a similar population of men. How man samples (at a minimum) should you plan on taking for your proposed study? You plan to work at a 95% confidence level. You are willing to accept an error of +/- 5 mmHg

Answer 1

The formula for margin of error is m = (z^*)*σ/sqrt(n)  

 

For a 95% confidence level z^* = 1.96, it is given that σ = 16.5, and you want m <= 5.  So

 

1.96*16.5/sqrt(n) <= 5

sqrt(n) >= 1.96*16.5 / 5

sqrt(n) >= 6.468

n >= 41.8

 

so take at least 42 samples