To solve this problem, we make use of the z statistic. We are to look for the bottom 8% who has the shortest lifespan, this is equivalent to a proportion of P = 0.08. Using the standard distribution tables for z, the value of z corresponding to this P value is:
z = -1.4
Now given the z and standard deviation s and the mean u, we can calculate for the number of years of the shortest lifespan:
x = z s + u
x = -1.4 (0.7) + 2.4
x = -0.98 + 2.4
x = 1.42 years
Therefore the life span is less than about 1.42 years