Elementary Statistics (12th Edition)

The mean can be counted by summing all the data and dividing it by the number of data: $\frac{1550+1642+1538+1497+1571}{5}=1559.6.$ Standard deviation=$\sqrt{\frac{\sum (x-\mu)^2}{n-1}}=\sqrt{\frac{(1550-1559.6)^2+...+(1571-1559.6)^2}{4}}=53.38.$ $z=\frac{value-mean}{standard \ deviation}=\frac{1642-1559.6}{53.38}=1.54.$ The z-score is between -2 and 2, hence it is not unusual.