The proportion of carbon monoxide in exhaust gases has an upper specification limit of 0.30. Emission control devices are being tested to meet such requirements. We wish that devices with an average carbon monoxide content of 0.15 or less be accepted 95% of the time. If the average carbon monoxide content is 0.34 or more, we wish the probability of acceptance to be 0.20. An estimate of the standard deviation of the proportion of carbon monoxide is 0.25. Find a variable sampling plan and explain its operation.