Consider the accompanying data on flexural strength (MPa) for concrete beams of a certain type. 5.5 7.2 7.3 6.3 8.1 6.8 7.0 7.5 6.8 6.5 7.0 6.3 7.9 9.0 8.6 8.7 7.8 9.7 7.4 7.7 9.7 8.0 7.7 11.6 11.3 11.8 10.7 The data below give accompanying strength observations for cylinders. 6.1 5.8 7.8 7.1 7.2 9.2 6.6 8.3 7.0 8.0 7.1 8.1 7.4 8.5 8.9 9.8 9.7 14.1 12.6 11.3 Prior to obtaining data, denote the beam strengths by X, ...,X, and the cylinder strengths by Y,..., Y. Suppose that the X's constitute a random sample from a distribution with mean and standard deviation and that the Y's form a random sample (independent of the X/'s) from another distribution with mean and standard deviation 2. (a) Use rules of expected value to show that X - Y is an unbiased estimator of - O E(X)= E(X) - E(Y) = H-2 O EX- E(X)- E(Y) -441-42 nm E(X) = E(X) - E(Y) = H - H - | E(X) = (E(X) - E() = 1-2 E(X) = nm (E(X) - E()) = H Calculate the estimate for the given data. (Round your answer to three decimal places.) -0.386 MPa (b) Use rules of variance to obtain an expression for the variance and standard deviation (standard error) of the estimator in part (a). v(x-x) = v(x) + v(n 2 2 =x + x of 1 n2 02 42 --m(ex-)- Calculate the estimate for the given data. (Round your answer to three decimal places.) -0.386 MPa (b) Use rules of variance to obtain an expression for the variance and standard deviation (standard error) of the estimator in part (a). v(x - x) = v(x) + v(n 2 2 171 022 n2 022 "2 Compute the estimated standard error. (Round your answer to three decimal places.) MPa (c) Calculate a point estimate of the ratio o/2 of the two standard deviations. (Round your answer to three decimal places.) (d) Suppose a single beam and a single cylinder are randomly selected. Calculate a point estimate of the variance of the difference X - Y between beam strength and cylinder strength. (Round your answer to two decimal places.) MPa 2