The minimum sample size required to estimate the mean usage of water = 2225.07
What is Standard deviation?
In statistics, the standard deviation (SD, also represented by the Greek letter sigma σ or the Latin letter s) is a measure that is used to quantify the amount of variation or dispersion of a set of data values.
We can find the minimum sample size required to estimate the mean usage of water as shown below:
Standard deviation 
Margin of error E=0.15
Critical value for 95% confidence interval = 1.96
Required minimum sample size: 

=2225.07
Hence, the minimum sample size required to estimate the mean usage of water = 2225.07
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Let x be the larger number and y be the smaller number.
Using the given info, we get
x = 4y - 2
We also know that
x + y = 18
Substitute x = 4y -2 into x + y = 18
(4y -2) +y = 18
5y - 2 = 18
5y = 20
y = 4
Enter this value into x = 4y - 2
x = 4(4) - 2
x = 14
The larger number is 14 and the smaller one is 4.
Answer:605052^11
Step-by-step explanation:
2x - 6y = 14
2x = 6y + 14
x = 3y + 7.....so sub in 3y + 7 for x in the other equation
4x - y = 9
4(3y + 7) - y = 9
12y + 28 - y = 9
12y - y = 9 - 28
11y = - 19
y = -19/11
x = 3y + 7
x = 3(-19/11) + 7
x = -57/11 + 7
x = -57/11 + 77/11
x = 20/11
solution is : (20/11, -19/11) <==