Chapter 6.2, Problem 30PB

Quartiles and outliers Refer to the previous exercise.

1. a. Find the z-score corresponding to the lower quartile (Q1) of a normal distribution.
2. b. Find and interpret the lower quartile and upper quartile of the MDI.
3. c. Find the interquartile range (IQR) of MDI scores.
4. d. Section 2.5 defined an observation to be a potential outlier if it is more than 1.5 × IQR below Q1 or

6.29 MDI The Mental Development Index (MDI) of the Bayley Scales of Infant Development is a standardized measure used in observing infants over time. It is approximately normal with a mean of 100 and a standard deviation of 16.

1. a. What proportion of children has an MDI of (i) at least 120? (ii) at least 80?
2. b. Find the MDI score that is the 99th percentile.
3. c. Find the MDI score such that only 1% of the population has MDI below it.