Twelve locations were selected in a county where a steel plant is accused of air pollution. Sulfate levels were measured at each of these locations as well as the distance of the location from the steel plant. The data were analyzed to see whether the sulfate level decreases as distance from the plant increases. What type of study is this?

List the 10 possible samples (without replacement) of size 3 3 that can be obtained from the population of five officials.

The number of chocolate chips in an 18-ounce bag of chocolate chip cookies is approximately normally distributed with a mean of 1252 chips and standard deviation 129 chips. (a) what is the probability that a randomly selected bag contains between 1100 and 1500 chocolate chips, inclusive? (b) what is the probability that a randomly selected bag contains fewer than 1125 chocolate chips? (c) what proportion of bags contains more than 1225 chocolate chips? (d) what is the percentile rank of a bag that contains 1425 chocolate chips?

2x minus y equals 6, x plus y equals negative 3