Use the Sign Test to answer:

Below is a "sample" of 20 airfares (in Canadian dollars) to various destinations as advertised by Northwest Airlines during their spring sale. [Source: Globe and Mail, March 1, 1993] (Note: data values have been sorted below to help calculations)

49 59 69 89 89 89 99 99 99 109 109 109 119 119 149 149 149 149 149 169

(a) Test at a = 0.10 if the median airfare for Northwest Airlines' flights during the spring sale is below $120.

(b) What is there about this data that might invalidate your conclusion in (a)?