## Elementary Statistics (12th Edition)

Here, n=370 and p=0.2. a) Mean=$n\cdot p=370 \cdot 0.2=74$. Standard deviation: $\sqrt{n \cdot p \cdot (1-p)}=\sqrt{370 \cdot 0.2 \cdot 0.8}=7.7.$ b) If a value is unusual, then it is more than two standard deviations far from the mean. $Minimum \ usual \ value=mean-2\cdot(standard \ deviation)=74-2\cdot7.7=58.6$ $Maximum \ usual \ value=mean+2\cdot(standard \ deviation)=74+2\cdot7.7=89.6$. 90 is more than the upper bound, therefore it is unusually high.