If the number of success or the number of failures is less than 10, then the confidence interval has a far less success rate in capturing the population parameter. Fortunately, there is a simple alternative procedure, know as "plus-four", that works remarkably well. The idea of the plus-four interval is to pretend that the sample contained two more "successes" and two more"failures" than it actually did, and then carry on like always. If the sample proportion is p=x/n where x represents the number of success and n represent the sample size. Then the modified sample proportion after including the fictional successes and failures is denoted by

p= (x+ 2)/(n+ 4)

The plus-four 95% confidence interval is therefore:

p 1.96 . p(1p) / n+ 4 (SQUARE ROOT)

Question : Let p= 3/10. Compute p.