suppose 500 coins are tossed using the normal curve approximation, find the probability of getting exactly 250 heads Solution answer is 0.032 as there\'s an equal probability of heads and tails. In the binomial distribution, p = 0.5, the number of \"successes\", i.e. heads. Also you have n = 500, the number of trials. The mean of this binomial distribution is np = 250 and the variance is np(1 - p) = 125. Standard deviation = sqrt(variance) = 11.2 For large n, it can be approximated by a normal distribution of the same mean and variance. I\'m not going to do it for you, but it involves calculating a value usually called z and looking up a table of the standard normal distribution..