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EXAMPLE 4

In a survey of 1011 people, 52% said that television is their main source of news. EXAMPLE 4. Find a margin of error. MEDIA SURVEY. What is the margin of error for the survey?.

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EXAMPLE 4

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  1. In a survey of 1011 people, 52% said that television is their main source of news. EXAMPLE 4 Find a margin of error MEDIA SURVEY • What is the margin of error for the survey? • Give an interval that is likely to contain the exact percent of all peoplewho use television as their main source of news.

  2. 1 = n = 0.031 + + + + – – – – 1 The margin of error for the survey is about 3.1%. ANSWER 1011 EXAMPLE 4 Find a margin of error SOLUTION • Use the margin of error formula. Margin of error Write margin of error formula. Substitute 1011for n. Use a calculator.

  3. It is likely that the exact percent of all people who use television as their main source of news is between 48.9% and 55.1%. ANSWER EXAMPLE 4 Find a margin of error • To find the interval, subtract and add 3.1% to the percent of people surveyed who said television is their main source of news (52%). 52% – 3.1% = 48.9% 52% + 3.1% = 55.1%

  4. D B A The correct answer is C. ANSWER C 1 n n n + + + + – – – – 1 = 0.05 1 = 0.05 Substitute for margin error. 0.0025 = EXAMPLE 5 Standardized Test Practice SOLUTION Use the margin of error formula. Margin of error Write margin of error formula. Square each side. n=400 Solve for n. There were 400 people surveyed.

  5. 3. INTERNET: In a survey of 1202 people, 11% said that they use the Internet or e-mail more than 10 hours per week. What is the margin of error for the survey? How many people would need to be surveyed to reduce the margin of error to 2%? + – ANSWER + – 2500 people need to be surveyed. The margin of error for the survey is about 2.9%. for Examples 4 and 5 GUIDED PRACTICE

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