Investigators take a sample of DINKS (dual-income families-where husband and wife both work-and no kids). The investigators have data on the husband's in-

come and the wife's income. By definition, family income = husband's income + wife's income.

The average family income was around $85,000, and 10% of the couples had fam-

ily income in the range $80,000-$90,000. Fill in the blanks, using the options given below, and explain briefly.

(a) The correlation between wife's income and family income is ______.

(b) Among couples whose family income is in the range $80,000-$90,000, the correlation between wife's income and husband's income is ______. P-698