Paper 1 · confidence intervals / Central Limit Theorem

120 bags of mealie-meal have mean mass 750g and standard deviation 3.9g. Using a 95% confidence interval with $z = 1.96$ , what is the upper bound of the confidence interval for the mean mass, in grams, correct to 2 decimal places?

A749.30 g

B750.70 g

C750.35 g

D751.40 g

Explanation: The margin of error is

1.96 \times 3.9/\sqrt{120} = 1.96 \times 0.356 = 0.698

g, so the upper bound is

750 + 0.698 = 750.70

Derived from ZIMSEC Statistics Paper 1, November 2021, Q1

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