When using mental math to solve problems with decimals, it is harder to keep track of what number goes where and where the decimal spot goes as well. Although, with whole numbers in mental math, it is a lot easier to solve since there is no decimal and less numbers (unless you are doing whole number math with a large amount of numbers).
Answer:
The 95% confidence interval for the proportion of water specimens that contain detectable levels of lead is (0.472,0.766).
Step-by-step explanation:
In a sample with a number n of people surveyed with a probability of a success of
, and a confidence level of
, we have the following confidence interval of proportions.

In which
z is the zscore that has a pvalue of
.
In a sample of 42 water specimens taken from a construction site, 26 contained detectable levels of lead.
This means that 
95% confidence level
So
, z is the value of Z that has a pvalue of
, so
.
The lower limit of this interval is:

The upper limit of this interval is:

The 95% confidence interval for the proportion of water specimens that contain detectable levels of lead is (0.472,0.766).
2x-1/2=3-x
x2 x2
2x-1=3-2x
+1 +1
2x=4-2x
+2x +2x
4x=4
/4 /4
x=1
Step-by-step explanation:
...x=+2...
...y=-3...