In a study of the effect of cooling rate on the hardness of welded joints, 50 welds cooled at a rate of 10oC/s had an average Rockwell (B) hardness of 91.1 and a standard deviation of 6.44, and 40 welds cooled at a rate of 30oC/s had an average hardness of 90.7 and a standard deviation of 4.18. Ten more welds will be made in order to increase the precision of the confidence interval. Which would increase the precision the most, cooling all 10 welds at the rate of 10oC/s, cooling all 10 welds at the rate of 30oC/s, or cooling 5 welds at 10oC/s and 5 at 30oC/s? Explain.