Building confidence interval under either t or z distribution

Q4
A system consists of five identical components connected in series as shown:

As soon as one component fails, the entire system will fail. Suppose each component has a lifetime that is exponentially distributed with meanλ = 2 years and that component fail independently of one another.
I. What is the probabilitythat the first component is still working after 1 year?
II. What is the probability that the entire system fails in 1 year?

Q5
The monthly starting salaries of students who receive an MBA degree have a standard deviationof $70. What sample size should be selected so that there is a 95% confidence of estimating the mean monthly within a samplingerror of $ 18 or less?

Q6
The compressive strength of a concrete is being used by an engineer and the results were recorded as follows:
221, 222, 231, 223, 230, 215, 210
Construct a 95% confidence intervalon the mean strength.

The solution gives detailed steps on finding the probability and building confidence interval under either t or z distribution.