The [tex] (1-\alpha )100\% [/tex] confidence interval for mean is
[tex] \mu \pm z_{\alpha/2} \frac{\sigma}{\sqrt{n} } [/tex].
Here [tex] \alpha =0.1 [/tex].
Use standard normal distribution table.
The z value to be used is such that
[tex] P(Z<z)=\alpha /2 [/tex]
[tex] P(Z<z)=0.05 [/tex]
z=-1.96
The z value to be used is 1.96.
