The slant shear test is widely accepted for evaluating the bond of resinous repair materials to concrete; it utilizes cylinder specimens made of two identical halves bonded at 30°. For 12 specimens prepared using wire-brushing, the sample mean shear strength (N/mm2) and sample standard deviation were 19.06 and 1.74, respectively, whereas for 12 hand-chiseled specimens, the corresponding values were 24.6 and 3.96. Does the true average strength appear to be different for the two methods of surface preparation? Test the relevant hypotheses using a significance level of .05. (Give ? to exact integer and t to 2 decimal places.)
a.) ? = ?
b.) t (?wire - ?hand) = ?