A study of the effect of television commercials on 12-year-old children measured their attention span, in seconds. The commercials were for clothes, food, and toys.


Clothes Food Toys
20 33 55
24 43 53
35 34 40
35 50 44
28 47 63
31 42 53
17 34 48
31 43 58
20 57 47
47 51
44 51
54

a. What are the null and alternate hypotheses?