Answer:
answer: At age 71.78 86% of the payments of the plan participants will be ceased
Step-by-step explanation:
Let X be the age at which a person dies. We know that X has a normal distribution with mean 68 and standard deviation 3.5. REcall that the expression P(X<=x) means the probability that a person dies before the age x. In order for us to do the calculations, we consider the random variable Z = (X-68)/3.5. The variable Z will be normally distributed with mean 0 and standard deviation 1 (i.e will be a standard normal distribution). Based on that, we would like to calculate the Z value for which we have 86% of the curve on the left of the value. Using a standard normal distribution table, we can find the z value corresponding to the 86% of the curve, which is aproximately 1.08. Then, the age we are looking for is 1.08*3.5+68 = 71.78 years