Using the definition of a confidence interval, it is found that the 90% confidence interval for the average cost for healthcare of a senior citizen receiving Medicare is ($12,000, $14,000).
A confidence interval is the sample mean plus/minus the margin of error.
Hence:
$13,000 - $1,000 = $13,000
$13,000 + $1,000 = $14,000
The interval is ($12,000, $14,000).
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