Next section: Difference between proportions

Therefore to compute the probability of 10 or more successes, compute the area above 9.5 successes. In terms of proportions, 9.5 successes is 9.5/20 = 0.475. Therefore, 9.5 = (0.475 - 0.40)/.11 = 0.682 standard deviations above the mean. The probability of being 0.682 or more standard deviations above the mean is 0.247 rather than the 0.182 that was obtained previously.The exact answer calculated using the binomial distribution is 0.245. For small sample sizes the correction can make a much bigger difference than it did here.

Next section: Difference between proportions