x1 = 18, n1 = 40, x2 = 30, n2 = 40; left-tailed test, α = 0.10; 80% confidence interval
a. Determine the sample proportions.
b. Decide whether using the two-proportions z-procedures is appropriate. If so, also do parts (c) and (d).
c. Use the two-proportions z-test to conduct the required hypothesis test.
d. Use the two-proportions z-interval procedure to find the specified confidence interval.