Question

2. Ten randomly selected construction laborers were asked how long the compressive strength of a concrete exposed to chemicals last before it corrodes. The mean time was 8.1 days, and the standard deviation was 0.81 days. Find the 99% confidence interval of the mean time. Assume the variable is normally distributed

Answer 1

We have given that,          
          
Sample mean =8.1  
Sample standard deviation =0.81
Sample size =10  
Level of significance=0.01  
Degree of freedom =9  
          
t critical value is (by using t table)=   3.2498  
          
Confidence interval formula is

$\bar{x}\pm t*\frac{S}{\sqrt{n}}=8.1\pm 3.2498*\frac{0.81}{\sqrt{10}}=(7.27,8.93)$
          
          
          
Conclusion: We are 99% confident that population mean time is between 7.27 days to 8.93 days.