The answer is b because you can divide them by 2 to get the answer<span />
Answer:
The correct option is (C) (2.769, 3.231).
Step-by-step explanation:
The confidence interval for mean when the standard deviation is not known is:

Given:

Compute the critical value as follows:

**Use a <em>t</em>-table.
The 95% confidence interval for true mean length of the bolt is:

Thus, the 95% confidence interval for true mean length of the bolt is (2.769, 3.231).
The correct option is (C).
This is actually easy, because you just have to add up the 25 +15 and that would get you 40. Then you would have to add 20 to the 40 and that would be 60, so that would make 40/60 chance that she wouldn't get blue.
And if you need it in a percentage, then you can just convert this into a percentage which would be, 66.666666666667%, also known as 66.67%