QCEVault

Interval estimates for proportions — Question 321

Original QCE Vault practice · 4 marks

Q321 · Practice questionTechnology-activeSimple familiar4 marks

QUESTION 321 (4 marks)

From 225225 independent responses, 144144 people choose option A. A student writes the 95%95\% interval as 0.64±1.960.64(0.36)/2250.64\pm1.96\sqrt{0.64(0.36)}/225.
a)
Identify the error in this expression.
[1 mark]
b)
Write the correct interval and calculate its endpoints to three decimal places.
[2 marks]
c)
Explain the effect of the error on the interval width.
[1 mark]
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