Practise forming approximate confidence intervals for population proportions and using interval limits to interpret claims.
In a survey, a random sample of 250 adults in Fromleigh were asked to fill in a questionnaire about their travel.
It was found that 102 adults in the sample travel by bus. Find an approximate 90% confidence interval for the proportion of all the adults in Fromleigh who travel by bus.
p^=250102=0.408,250p^(1−p^)=2501022501482501=0.000966144.p^±z0.000966144,z=1.645.
Confidence interval: 0.357 to 0.459 (3 s.f.).
M1 for correct form using a z-value;
B1 for z=1.645;
A1 for the interval.