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In a comparison of the cleaning action of four detergents, 2t] pieces of white cloth were first soiled with India ink. The cloths were then washed under controlled conditions with 5 pieces washed by each of the detergents. Unfortunately, three pieces of cloth were 'lost' in the course of' the experiment. Whiteness readings, made on the 1'! remaining pieces of cloth, are shown below. Assuming all whiteness readings to he normally distributed with common variance, test the hypothesis of no difference between the four brands as regard rnean whiteness readings after washing