Answer:
A sample of 18 is required.
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 Z-table as such z has a p-value of
.
That is z with a pvalue of
, so Z = 1.88.
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 indicated that the standard deviation was 2.2 days.
This means that 
How large a sample must be selected if the company wants to be 92% confident that the true mean differs from the sample mean by no more than 1 day?
This is n for which M = 1. So



Rounding up:
A sample of 18 is required.
74746394738284729274638292
2/21, 16/28
Multiply by 2,3,4
Answer:
6 1/4
Step-by-step explanation:
Total length of the ribbon= 15 3/4 m= 63/4 m
One piece= 9 1/2 m= 19/2 m
Other piece length =X
X= 63/4-19/2
=63/4-38/4
=25/4
=6 1/4
Step-by-step explanation:
I am not sure what you want to calculate as ultimate goal.
but your have an error already in your third line in the picture.
(3-6i)(2-4i) = 3×(2-4i) - 6i(2-4i)
you had there a "+" instead of a "-".
and then you made subsequent mistakes in every line, some of them are funnily bringing you more back to the real result (e.g. -12i + 12i would be 0 and not -24i, but if the third line would have been correct, then yes, -24i is actually needed) - but not completely.
= 3×2 - 3×4i - 6i×2 + 6i×4i =
= 6 - 12i - 12i + 24×-1 = 6 - 24i - 24 = -24i - 18
then in the last 3 lines you kind of lose it completely. I am absolutely not sure, what you are calculating, and where the "+" cube from instead of "×" (multiplications) and such.
(3+6i)(2+4i) = 3×2 + 3×4i + 6i×2 + 6i×4i =
= 6 + 12i + 12i + 24×-1 =
= 6 + 24i - 24 = 24i - 18
is that what you wanted to show ?