The mean absolute deviation (MAD) for the first set of data is 1.2 and the MAD for the second set of data is 0.4. Approximately how many times the variability in the heights of the seventh graders is the variability in the heights of the sixth graders? (Round all values to the tenths place.)
+33653 You probably take the ratio of the two MADs, so either 1.2/0.4 or 0.4/1.2 depending on which applies to seventh graders and which to sixth graders, which you don't specify!
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+118658 if 6th graders MAD=0.4
and 7th graders MAD=1.2
I think the 7th graders are 3 times more variable in height. 
Jacob wants to know how many students in his school enjoy watching space travel programs on TV. He poses this question to all 20 students in his history class and finds that 80% of his classmates enjoy watching space travel programs on TV. He claims that 80% of the school's student population would be expected to enjoy watching space travel programs on TV. Is Jacob making a valid inference about this population?
No, it is not a valid inference because his classmates do not make up a random sample of the students in the school
No, it is not a valid inference because he asked all 20 students in his history class instead of taking a sample from his math class
Yes, it is a valid inference because his classmates make up a random sample of the students in the school
Yes, it is a valid inference because he asked all 20 students in his history class
