Passage Summary: A marketing agent says that 90 percent of their clients who actually made money last year made over $100,000. Since no one used to make more than $10,000, the agent claims 90 percent of all their clients must have increased their profits tenfold.

Conclusion: Ninety percent of the agent's entire client base saw their profits grow by at least ten times last year.

Reasoning: Among the clients who were profitable, 90 percent hit the $100,000 mark, whereas in the past, no client made more than $10,000.

Analysis: The agent makes a huge leap from '90 percent of those who made a profit' to '90 percent of all clients.' If only a small fraction of clients made any profit at all, then the '90 percent of profitable clients' could be a tiny percentage of the total group. This is a classic sampling error where a subset is confused with the whole population. Look for an answer that points out this failure to account for clients who didn't make a profit.