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A survey was given to a random sample of voters in the United States to ask about their preference for a presidential candidate. The percentage of people who said they preferred Candidate A was 
80%. The margin of error for the survey was 
4%. Write a confidence interval for the percentage of the population that supports Candidate A.

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A survey was given to a random sample of voters in the United States to ask about their preference for a presidential candidate. The percentage of people who said they preferred Candidate A was 80% 80 \% . The margin of error for the survey was 4% 4 \% . Write a confidence interval for the percentage of the population that supports Candidate A.

Full solution

Q. A survey was given to a random sample of voters in the United States to ask about their preference for a presidential candidate. The percentage of people who said they preferred Candidate A was 80% 80 \% . The margin of error for the survey was 4% 4 \% . Write a confidence interval for the percentage of the population that supports Candidate A.
  1. Understand Confidence Interval: Understand the concept of a confidence interval. A confidence interval gives a range of values within which we can say with a certain level of confidence that the true population parameter lies. In this case, we are looking for the interval around the survey percentage that includes the true percentage of the population that supports Candidate A.
  2. Calculate Lower Bound: Calculate the lower bound of the confidence interval.\newlineTo find the lower bound, we subtract the margin of error from the survey percentage.\newlineLower bound =Survey percentageMargin of error= \text{Survey percentage} - \text{Margin of error}\newlineLower bound =80%4%= 80\% - 4\%\newlineLower bound =76%= 76\%
  3. Calculate Upper Bound: Calculate the upper bound of the confidence interval.\newlineTo find the upper bound, we add the margin of error to the survey percentage.\newlineUpper bound =Survey percentage+Margin of error= \text{Survey percentage} + \text{Margin of error}\newlineUpper bound =80%+4%= 80\% + 4\%\newlineUpper bound =84%= 84\%
  4. Write Confidence Interval: Write the confidence interval.\newlineThe confidence interval is written as a pair of values, the lower bound and the upper bound.\newlineConfidence interval = (Lower bound,Upper bound)(\text{Lower bound}, \text{Upper bound})\newlineConfidence interval = (76%,84%)(76\%, 84\%)

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