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.
41% of students ran in 12 minutes or less.
Using the histogram we see that there were 2+12+11+9=34 students that ran. Out of those, 2+12=14 ran in 12 minutes or less (the first two bars).
14/34 = 0.411 = 41%.
The polynomial x3+8 is equal to (x+2)(x2-2x+4)
Innermost orbitals have the least amount of energy
Diametre = 2 x Radius
Radius = 7
Circumference = 2πr
= 2x22/7x7
= 44