A sample of 30 lap times has mean 25.3 minutes and standard deviation 1.218 minutes. Testing $H_0:\mu=25$ against $H_1:\mu>25$ , what is the value of the test statistic?

-1.35

0.25

1.35

1.65

Explanation:

z = \dfrac{\bar x - \mu_0}{s/\sqrt n} = \dfrac{25.3-25}{1.218/\sqrt{30}} = \dfrac{0.3}{0.2224} \approx 1.35

. Forgetting to divide the standard deviation by

\sqrt n

gives

0.3/1.218\approx0.25

. Reversing the subtraction order gives

-1.35

. Quoting the 5% one-tailed critical value instead of the computed statistic gives

1.65

Derived from ZIMSEC Maths Paper 1, June 2007, Q10 (Statistics)

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