Answer
a) Mean:74. Standard deviation:7.38.
b)It is unusually high.
Work Step by Step
Here, n=370 and p=0.2.
a) Mean=$n\cdot p=370 \cdot 0.2=74$.
Standard deviation: $\sqrt{n \cdot p \cdot (1-p)}=\sqrt{340 \cdot 0.2 \cdot 0.8}=7.38.$
b) If a value is unusual, then it is more than two standard deviations far from the mean. $Minimum \ usual \ value=mean-2\cdot(standard \ deviation)=74-2\cdot7.38=59.24$
$Maximum \ usual \ value=mean+2\cdot(standard \ deviation)=74+2\cdot7.38=88.76$.
90 is more than the upper bound, therefore it is unusually high.
