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4.5 Statistical distributions (A-level only)

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Question 20

The length of steel bolts produced by a machine is normally distributed with a mean of 50.0 mm and a standard deviation of 0.8 mm.

a.

Find the probability of a bolt being longer than 51.5 mm.

[2]
b.

The technician suspects that the mean length of the bolts has changed.

Write down a null and alternative hypothesis for a two-tailed test.

[1]
c.

A sample of 16 bolts is measured and the mean length is found to be 50.5 mm.

Test at the 10% significance level whether there is evidence that the mean length has changed.

[3]

4.5 Statistical distributions (A-level only) Questions

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  3. /4.5 Statistical distributions (A-level only)