A researcher wished to estimate the difference between the proportion of users of two

shampoos who are satisfied with the product. In a sample of 400 users of Shampoo A

taken by this researcher, 78 said they are satisfied. In another sample of 500 users of

Shampoo B taken by the same researcher, 92 said they were satisfied.

Construct a 90% confidence interval for the true difference between the two population proportions.