Answer:
x = 16.5
Step-by-step explanation:
Use pythagorean theorem
a² + b² = c²
Plug in terms
7.1² + x² = 18²
Square each term
50.41 + x² = 324
Subtract a from c
x² = 273.59
Find square root
16.5
Given a series, the ratio test implies finding the following limit:

If r<1 then the series converges, if r>1 the series diverges and if r=1 the test is inconclusive and we can't assure if the series converges or diverges. So let's see the terms in this limit:

Then the limit is:

We can simplify the expressions inside the absolute value:

Since none of the terms inside the absolute value can be negative we can write this with out it:

Now let's re-writte n/(n+1):

Then the limit we have to find is:

Note that the limit of 1/n when n tends to infinite is 0 so we get:

So from the test ratio r=0.4 and the series converges. Then the answer is the second option.
Answer:


Step-by-step explanation:
Notation
represent the sample mean
population mean (variable of interest)
s represent the sample standard deviation
n represent the sample size
Solution to the problem
The confidence interval for the mean is given by the following formula:
(1)
For this case the 9% confidence interval is given by:

We can calculate the mean with the following:

And we can find the margin of error with:

The margin of error for this case is given by:

And we can solve for the standard error:

The critical value for 95% confidence using the normal standard distribution is approximately 1.96 and replacing we got:

Now for the 98% confidence interval the significance is
and
the critical value would be 2.326 and then the confidence interval would be:


Answer: 41.5
hope this helps!