Hi!
When the mean ([tex]\bar{x}[/tex]), the number of samples (n) and standard deviation (σ) are known, you can apply the following equation to determine confidence intervals. The value of z at 90% confidence can be found in tables (It is 1,645).
[tex](\bar{x}-z* \frac{\sigma}{ \sqrt{n} },\bar{x}+z* \frac{\sigma}{ \sqrt{n} }) \\ \\ (14-1,645* \frac{2,50}{ \sqrt{10} },14+1,645* \frac{2,50}{ \sqrt{10} } \\ \\ (12,70\$;15,30\$) [/tex]
Have a nice day!
