You read a report that says on the basis of a random sample

You read a report that says “on the basis of a random sample of 25 rats, a confidence interval for the true mean survival time extends from 13.45 days to 14.15 days.” The confidence level for this interval is A. 90% *B. 95% C. 98% D. 99%

Solution

Given :

Confidence intervals (13.45, 14.15)

n= 25

To find : Confidence level

Solution :

Lower bound= x bar- ME= 13.45

Upper bound = z bar + ME= 14.15

Solving the above two equations algebraically, we get ME= 13.8

So, Decreasing the sample size Increases the margin of error.

Therefore the relationship, \'\'Margin of the error=+/- confidence coeffcient+ standard error\'\' explains how many standard errors has to be added or subtrated.

So we add and subtract 2 standard errors

The rule of thumb says , If wee add and subtract 2 standard errors we would be confident 95%

So the answer is B.95%