Answer:
A sample of 179 is needed.
Step-by-step explanation:
We have that to find our
level, that is the subtraction of 1 by the confidence interval divided by 2. So:

Now, we have to find z in the Ztable as such z has a pvalue of
.
That is z with a pvalue of
, so Z = 1.44.
Now, find the margin of error M as such

In which
is the standard deviation of the population and n is the size of the sample.
A previous study found that for an average family the variance is 1.69 gallon?
This means that 
If they are using a 85% level of confidence, how large of a sample is required to estimate the mean usage of water?
A sample of n is needed, and n is found for M = 0.14. So






Rounding up
A sample of 179 is needed.
The area formula for rectangles is lxw. To solve, I would divide the figure up into 3 rectangles- top,middle and bottom, then find the areas and add them together.
Top: 4x13=52 cm^2
Middle: 5x8=40 cm^2
Bottom: 21x10=210 cm^2
(5 is the width of the middle piece. You get it from subtracting. 21-8-8=5. 13 is the width of the top piece. 5+8=13)
52+40+210
=302 cm^2
So your answer is 302 square centimetres.
Call the region in the

-

plane, bounded by

and

,

. Then the volume under the given surface is
Answer: 
Step-by-step explanation:



=

=
=

=

Answer- 