22. In Example 11, Table 6.7 (page 270), the positive association between family income and SAT score is clear from the lockstep pattern, but to calculate a specific numerical value for the correlation, we need to make a simplifying assumption. For each income bracket with fixed endpoints, choose its midpoint. Now, use a calculator (or Excel) to calculate a correlation value (refer to Spotlight 6.2 on page 259).