Question 515704
In general, you can approximate a binomial distribution with a normal distribution with the same mean and standard deviation if the expected number of successes and failures are both at least 5 (some texts use a larger number, but 5 is most common).

If n is the number of experiments and p is the probability of success with each experiment, then np is the expected number of successes after n experiments.  In this case:

np = (84)(0.94) = 78.96 successes

which is certainly greater than or equal to 5, so our expected number of successes is high enough to use the normal approximation.  If p is the probability of success, then q = 1 - p is the probability of failure.  For this problem,

q = 1 - p = 1 - 0.94 = 0.06

which is quite small.  The expected number of failures after n experiments would be nq, which in this case gives us:

nq = (84)(0.06) = 5.04 failures

So the expected number of failures is just high enough to use the normal approximation.  In other words, because the expected number of successes and failures are both greater than or equal to 5, the binomial distribution with n = 84 and p = 0.94 will be bell-curve shaped enough to justify approximating it with the normal distribution.