Question

If we wish to have a 95% confidence interval, what would be the value of the confidence coefficient?

Answer 1

http://mathworld.wolfram.com/ConfidenceInterval.html
$$
\mu-n\sigma<x<\mu+n\sigma
$$
Where \(\mu\) is the mean and \(\sigma\) is the standard deviation. So to compute the 95% confidence interval, you need both these values.

The link above that n=1.96 will provide the 95% confidence interval.

To determine in general to confidence coefficient for any probability P other than .95, use
$$
n=\sqrt 2 erf^{-1}(P)
$$
Where \(erf^{-1}(P)\) is the inverse error function evaluated at P.

For example, in your problem, P=.95 so http://www.wolframalpha.com/input/?i=%28inverse+error+function+.95%29*sqrt%282%29