Rice survey
p = 17/36 = 0.472 of farmers used 'Old' varieties
= 0.472 ± 0.166
This diagram uses 95% bounds on the error distribution (or at least the normal approximation to it) to find the 95% CI for the population proportion.
As part of a survey of rice producers in Sri Lanka, 36 farmers were randomly selected from 4 villages. Each sampled farmer was asked about the variety of rice that he used and the varieties were categorised as 'Old', 'Traditional' or 'New'. Seventeen of the 36 farmers in the survey used 'Old' varieties.