(a) 400 labourers were selected at random from a certain district. Their mean income was 140-5 dollar per month, with standard deviation 25-2 dollar. Set up 95% confidence limits within which the...

Extracted text: (a) 400 labourers were selected at random from a certain district. Their mean income was 140-5 dollar per month, with standard deviation 25-2 dollar. Set up 95% confidence limits within which the income of the labour community of district is expected to lie. (b) Set up 95% confidence limits for the standard deviation of the entire labour community of the district.