1. ## uuhh stumped

What is the value for X2left (chi-squared - left) for a 95% confidence interval when n=18?

Anyone? Like a foreign language to me..

2. I don't know what 'chi-squared - left' means.
A $\chi^2$ is a random variable.
I'll guess that you want a CI for $\sigma^2$, which is a constant.
CI's guess at constant.
Prediction Interval's guess at random variables.