Two methods, I and II, are available for determining the sulphur dioxide content of a soft drink. The variances associated with single determinations are and respectively, but it is usual to use several independent determinations with one of the two methods. Show that if I costs c times as much to carry out as II per determination, then I is only to be preferred if 020 >

c. Thirteen determinations were made using method I on one drink and thirteen using method II with another drink. The sample variances were equal. Show that, on the basis of this information, in order to be able to make a fairly confident decision about which method to use, one method would have to be at least 3-28 times as costly as the other. [Interpret 'fairly confident' as a 95% level of probability.] (Wales Maths.)