The student union is interested to know what proportion of students are in favour of moving the university campus to the city. They survey 120 students who are near the campus caf around lunchtime. 54 students say that they are in favour of a move to the city.

a)[5marks]Construct a 95% confidence interval for the proportion of students who support a move to the city.Show formulas used in calculations.

b)[4marks]Give an example of a potential source of bias this sampling scheme may suffer from. Explain how you could modify the sampling scheme to avoid this source of bias.