Chicken Delight claims that 89 percent of its orders are del

Chicken Delight claims that 89 percent of its orders are delivered within 10 minutes of the time the order is placed. A sample of 90 orders revealed that 76 were delivered within the promised time. At the .025 significance level, can we conclude that less than 89 percent of the orders are delivered in less than 10 minutes? What is the decision rule? Compute the value of the test statistic What is your decision regarding the null hypothesis?

Solution

(a) It is a left-tailed test.

Given a=0.025, the critical value is Z(0.025) = 1.96 (from standard normal table)

Reject Ho if Z<-1.96

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(b) The test statistic is

Z=(phat-p)/sqrt(p*(1-p)/n)

=(76/90-0.89)/sqrt(0.89*(1-0.89)/90)

=-1.38

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(c) Cannot reject Ho