An environmentalist wants to find out the fraction of oil tankers that have spil

Question

An environmentalist wants to find out the fraction of oil tankers that have spills each month.

Step 1 of 2: Suppose a sample of 198 tankers is drawn. Of these ships, 155 did not have spills. Using the data, estimate the proportion of oil tankers that had spills. Enter your answer as a fraction or a decimal number rounded to three decimal places.

__________

Step 2 of 2: Suppose a sample of 198 tankers is drawn. Of these ships, 155 did not have spills. Using the data, construct the 80% confidence interval for the population proportion of oil tankers that have spills each month. Round your answers to three decimal places.

Lower Endpoint:_____ Upper Endpoint:_____

Explanation / Answer

1) proportion of oil tankers that had spills phat=(198-155)/198 =43/198 =0.217

2)std error =(phat*(1-phat)/n)1/2 for n=198

=0.0293

for 80% CI ; z =1.2816

hence Lower Endpoint: sample proportion -z*Std error =0.180

Upper Endpoint : sample proportion +z*Std error =0.255

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