In the first week of July, a record 1100 people went to the local swimming pool. In the second week, 100 fewer people went to the pool than in the first week. In the third week, 150 more people went to the pool than in the second week. In the fourth week, 150 fewer people went to the pool than in the third week. What is the percent decrease in the number of people who went to the pool over these four weeks?