Thread: Confidence interval

The sulfur dioxide and nitrogen oxides are byproducts of fuel consumption. These are substances that can travel long distances and become acidic before settling in the form of "acid rain". The following data were obtained for the sulfur dioxide concentration (in micrograms per m3) in a Bavarian forest allegedly damaged by acid rain.
52.7 43.9 41.7 71.5 47.6 55, 1
62.2 56.5 33.4 61.8 54.3 50, 0
45.3 63.4 53.9 65.5 66.6 70, 0
52.4 38.6 46.1 44.4 60.7 56, 4
Assuming that the concentration of sulfur dioxide is a normal variable, construct a confidence interval of 95% for the average concentration. If on average the concentration of this compound in undamaged areas of the same country is 20 ug/m3, what can be said about the results?

I tried to solve:
n=23
standard deviation= 10,28591
average=20ug
z= 1, 96

then:
20-1,96*(10,28591/sqrt(23))<u<20+1,96*(10,28591/sqrt(23))
15,796<u<24,2037

is it correct?

I see it as n=24 and I am confused by the use of a comma for a decimal point.

I get