Since 68% of the distribution is within one standard deviation of the mean, this means that 68/2 = 34% of the distribution lies above the mean and is less than one standard deviation away from the mean.
The mean is the halfway point of any normal distribution, so 50% of the distribution lies below the mean.
So 50+34 = 84% distribution lies below the score of 172 because 172 is the point that is above the mean and it is one standard deviation away from the mean of 160.
