This problem was in the textbook. To find the probability of mu we have P(-0.96<Z<1.09)=0.69. So I reasoned the probability of at least for was (0.69)^4(0.31)+(0.69)^5. But the solution has 5*(0.69)^4(0.31)+(0.69)^5. Maybe it is just last, but I'm not sure why we are multiplying by five.