Answer:
The 90% confidence interval for the mean usage of electricity is between 17.4 kwH and 17.6 kwH
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 
So it is z with a pvalue of 1-0.05 = 0.95, so z = 1.645
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.
So

The lower end of the interval is the mean subtracted by M. So 17.5 - 0.14 = 17.4 kwH
The upper end of the interval is M added to the mean. So 17.5 + 0.14 = 17.6 kwH
The 90% confidence interval for the mean usage of electricity is between 17.4 kwH and 17.6 kwH
What is x in this situation?
let's firstly convert the mixed fraction to improper fraction, and then divide it by 4 to see what our quotient is.
![\bf \stackrel{mixed}{2\frac{1}{4}}\implies \cfrac{2\cdot 4+1}{4}\implies \stackrel{improper}{\cfrac{9}{4}} \\\\[-0.35em] ~\dotfill\\\\ \cfrac{9}{4}\div 4\implies \cfrac{9}{4}\div \cfrac{4}{1}\implies \cfrac{9}{4}\cdot \cfrac{1}{4}\implies \cfrac{9}{16}](https://tex.z-dn.net/?f=%5Cbf%20%5Cstackrel%7Bmixed%7D%7B2%5Cfrac%7B1%7D%7B4%7D%7D%5Cimplies%20%5Ccfrac%7B2%5Ccdot%204%2B1%7D%7B4%7D%5Cimplies%20%5Cstackrel%7Bimproper%7D%7B%5Ccfrac%7B9%7D%7B4%7D%7D%20%5C%5C%5C%5C%5B-0.35em%5D%20~%5Cdotfill%5C%5C%5C%5C%20%5Ccfrac%7B9%7D%7B4%7D%5Cdiv%204%5Cimplies%20%5Ccfrac%7B9%7D%7B4%7D%5Cdiv%20%5Ccfrac%7B4%7D%7B1%7D%5Cimplies%20%5Ccfrac%7B9%7D%7B4%7D%5Ccdot%20%5Ccfrac%7B1%7D%7B4%7D%5Cimplies%20%5Ccfrac%7B9%7D%7B16%7D)
Answer:
the price is 250
Step-by-step explanation:
let cp be x.
the marked price is 116x/100=1.16x.
25x/100=6250/100
x=250