GMAT Study Guide - a prep wikibook
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It can be best explained with this example:
In the United States, of the people who moved from one state to another when they retired, the percentage who retired to Florida has decreased by 3 percentage points over the past ten years. Since many local businesses in Florida cater to retirees, this decline is likely to have a noticeably negative economic effect on these businesses.
Which of the following, if true, most seriously weakens the argument?
A. Florida attracts more people who move from one state to another when they retire than does any other state.
B. The number of people who move out of Florida to accept employment in other states has increased over the past ten years.
C. There are far more local businesses in Florida that cater to tourists than there are local businesses that cater to retirees.
D. The total number of people who retired and moved to another state for their retirement has increased significantly over the past ten years.
E. The number of people who left Florida when they retired to live in another state was greater last year than it was ten years ago.
Guys this is a beauty. Please hammer this into your head. This is a standard percentage trap. Let me elaborate.
Assume that last year 1000 people in the US moved out of state to retire.
Of this say 10% moved to Florida = 100 people
So 90% moved to states other than Florida right?
This year 20000 people moved to other state to retire.
Of this say 8% moved to florida = 160 people.
So 92% moved to states other than Florida right?
Though the %of people moving to Florida has decreased (because %of people moving to otherstates has increased) number of people moving to Florida has infact increased from 100 to 160. So the local businesses are gonna do great.
The bold portion is what (D) says and thus weakens the argument more seriously than (C).