Resident: Data indicates that 30 percent of the houses in our town have indaequate site drainage and 30 percent have ...

on November 12, 2019

Hello @ca_teran1@yahoo.com,

You have a point, the flaw in this question is a misuse of percentages. However, it may be a different flaw than you expected. The error in this statement is that it fails to account for houses that have both problems - inadequate drainage and structural defects.

I'll input some numbers to explain.

Let's say there are 100 houses in the town.
Houses with only Structural Defects: 25
Houses with only Inadequate drainage: 25
Houses with both: 5

What percentage of houses have structural defects? 30/100 or 30%
What percentage of houses have inadequate drainage? 30/100 or 30%
What percentage of houses have some kind of problem? 55/100 or 55%

This proves that the conclusion is not necessarily true. It could be less than 60%. The resident in the stimulus assumed that these problems cannot overlap.