ATM's must be stocked with enough cash to satisfy customers making withdrawals over an entire weekend. But if too much cash is unnecessarily kept in the ATMs, the bank is forgoing the opportunity of investing the money and earning interest. Suppose that at a particular branch, the expected mean amount of money withdrawn from ATMs per customer over the weekend is $160. If a random sample of 36 customers transactions is examined and the sample mean withdrawal is $172 and the standard deviation is $30, is there evidence to believe that the population average withdrawal is no longer $160?

Use = .05.

TEST STATISTIC

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zcalc = X - U₀

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(s/square root of n)

Why is this the appropriate test statistic for this scenario?

Is this a one-or two-tailed hypothesis test? explain.

Z

Upper-Tailed Test Lower-Tailed Test Two-Tailed Test

0.01 2.326 -2.326 2.576

0.05 1.645 -1.645 1.960

0.10 1.282 -1.282 1.645

State the rejection region:

X = 172

u = 160

s - 30

n = 36

Zcalc = 2.40