## Elementary Statistics (12th Edition)

If a value is unusual, then it is more than two standard deviations far from the mean. $Minimum \ usual \ value=mean-2\cdot(standard \ deviation)=100-2\cdot15=70$ $Maximum \ usual \ value=mean+2\cdot(standard \ deviation)=100+2\cdot15=130$. Therefore the z scores are -2 and 2, the IQ scores are 70 and 130.