You would like to investigate whether smokers are more likely than nonsmokers to get lung cancer. You take the students in your class, select half at random and tell them to smoke a pack of cigarettes each day, and you tell the other half not to ever smoke. Fifty years from now, you will analyze whether more smokers than nonsmokers got lung cancer. Is this an experiment or an observational study?

Experiment

Explanation:

This would be an example of an experiment. This is an experiment because you are manipulating what the behaviour of the students is. A treatment is being applied to your subjects, as you are telling some of them to smoke and others not to. An observational study would require you not to interfere with the behaviour of the subjects, and simply observe what the outcome of their actions is in time.

19.

step-by-step explanation:

you add the 9 in the tens column since it is a single digit and 9 plus zero is 9 so it is 19

x + y = 90 5x – 10y = 90 90 – 10y = 5x 90 + 10y = 5x

step-by-step explanation:

last month maria hiked the 5-mile mountain trail a number of times and she hiked the 10-mile canal trail several times. let x represent the number of times she hiked the 5-mile trail, and let y represent the number of times she hiked the 10-mile trail. if she hiked a total of 90 miles, which equation can be used to find the number of times maria hiked each trail? x + y = 90 5x – 10y = 90 90 – 10y = 5x 90 + 10y = 5x