by aetos » Wed Jul 31, 2013 4:37 pm
Using a normal distribution table, you can see that .3 from the mean (meaning .5 + .3 = .8 or 80%) is .8425 standard deviation from the mean.
68 + .8425*4 = 71.37
80% are dead by the age of 71.37
This is probably the answer, considering how my work is usually impeccable.