For a group experiment, your science class measured the fine-particulate concentrations in the air at random places around campus, and estimated a sample average of 32 μg/m3 (micrograms per cubic meter). If 225 readings were taken, and the standard deviation of the sample measurements was 3 μg/m3, you are 99.7% confident that actual concentration of fine particulates at the school is __________ .

A. 31.7 μg/m3 – 32.3 μg/m3
B. 31.4 μg/m3 – 32.6 μg/m3
C. 26 μg/m3 – 38 μg/m3
D. 28 μg/m3 – 34 μg/m3

Question

For a group experiment, your science class measured the fine-particulate concentrations in the air at random places around campus, and estimated a sample average of 32 μg/m3 (micrograms per cubic meter). If 225 readings were taken, and the standard deviation of the sample measurements was 3 μg/m3, you are 99.7% confident that actual concentration of fine particulates at the school is __________ .

A.	31.7 μg/m3 – 32.3 μg/m3
B.	31.4 μg/m3 – 32.6 μg/m3
C.	26 μg/m3 – 38 μg/m3
D.	28 μg/m3 – 34 μg/m3

anonymous · Answer

99.7% C.I. is  mean +- 3 std errors of mean 

SE = SD/sqrt(225) = 3/15

32 +- 3 (3/15)  = 31.4 to 32.6 ug/m3  is answer