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daijiabj · 发表于 2006-10-30 16:18:00

Finding of a survey of Systems magazine subscribers: Thirty percent of all merchandise orders placed by subscribers in response to advertisements in the magazine last year were placed by subscribers under age thirty-five.

Finding of a survey of advertisers in Systems magazine: Most of the merchandise orders placed in response to advertisements in Systems last year were placed by people under age thirty-five.

For both of the findings to be accurate, which of the following must be true?

More subscribers to Systems who have never ordered merchandise in response to advertisements in the magazine are age thirty-five or over than are under age thirty-five.
Among subscribers to Systems, the proportion who are under age thirty-five was considerably lower last year than it is now.
Most merchandise orders placed in response to advertisements in Systems last year were placed by Systems subscribers over age thirty-five.
Last year, the average dollar amount of merchandise orders placed was less for subscribers under age thirty-five than for those age thirty-five or over.
Last year many people who placed orders for merchandise in response to advertisements in Systems were not subscribers to the magazine.