An experiment to compare the tensile strength of polymer-modified mortar with unmodified mortar resulted in a = 19.00 for modified mortar for 47 samples and in y = 16.51 for unmodified mortar for 33 samples. Let /1 and /2 be the true average tensile strengths for the modified and unmodified mortars. Assume the bond strength distributions are both normal with standard deviations o1 = 1.55 and 02 = 1.60 respectively. We will test Ho: #1 - /2 = 0 with Ha: /1 - /2 > 0 at significance level 0.01. Compute the standard deviation o applicable to this hypothesis test. Give your answer to 3 decimal places