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Solution:(a) Null hypothesis: There is no signiticant difference between the childuen who receive an audio visual presentation and those children who receive only the visual aspected of the advertisement with regard to the level of recall ofi.e, H_(0):u_(1)-u_(2)=0Alternative Hypothesis: Tneue is significant difference between the children who receive an audio vorual puesentation and thase children who receive only the visual aspat of the advertisement.i.e, H_(1):(u_(1)-u_(2))!=0(b) Given bar(x)_(1)=3.70 and bar(x)_(2)=3.30*s_(1)^(2)=(1.98)^(2),s_(2)^(2)=(2.13)^(2) under H_(0), the test statistic is:{:[t=(( bar(x)_(1)- bar(x)_(2)))/(sqrt(((s_(1)^(2))/(n_(1)))+((s_(2)^(2))/(n_(2)))))-t_(n_(1)+n_(2)-2)],[=(3.7-3.3)/(sqrt(((1.98)^(2))/(20))+(((2-13)^(2))/(20))))=0.6151]:}(c) The rejection region:|t| > t_(alpha//2)i.e. t < - ... See the full answer