a) In a standard normal distribution, what z-score has the property that 90% of the data fall between the z-score and its negative. In other words, find appositive z-score, a, such that

P(-a < x < a) = 0.90. Use the Standard table for this, not the Empirical rule.

Hint: this is just like the first step of the solution to #2 part c

b) In a standard normal distribution, find P(-2.55 < z < 2.55) (I used "z" instead of "x" because this is a standard normal distribution, but using "x" would have been a correct way to write it too.