Question

Find z α 2. Make a sketch and round to 3 decimals for each problem.
    a) for a 90% confidence interval
    b) for a 98% confidence interval
    c)  Find z α that separates the top 20%. Round to 3 decimal places.
d) Find z α for the first Quartile. Round to 3 decimal places.

Answer 1

Solution :

(a)

At 90% confidence level the z is ,

= 1 - 90% = 1 - 0.90 = 0.10

/ 2 = 0.10 / 2 = 0.05

Z_/2 = Z _0.05 = 1.645

(b)

At 98% confidence level the z is ,

= 1 - 98% = 1 - 0.98 = 0.02

/ 2 = 0.02 / 2 = 0.01

Z_/2 = Z _0.01 = 2.326

(c)

P(z > 0.842) = 0.20

z = 0.842

(d)

P(Z < -0.674) = 0.25