4. Two different ghting techniques are compared by measuring the intensity of light at selected locations in areas lighted by the two methods. Given that 15 measurements in the rst area had a standard deviation of 2.7 footcandles and 21 measurements in the second area had a standard deviation of 4.2 footcandles. (a) (5 points) 1What assumptions must be made as to how the two samples are obtained? [b] [10 points) Under the assumptions in part {a}, can it be concluded that the lighting in the second area is less uniform? Use a 0.01 level of signicance. Page 1 of 2 5. Pull-strength tests on 10 soldered leads for a semiconductor device yield the following results in poundsforce required to rupture the bound: 15.3, 12.7. 13.2, 1&9, 10.5, 13.3. 11.1, 14.3, 110, 125. Another set of 8 leads was tested after encapsulation to determine whether the pull strength has been increased by encapsulation of the device, with the following results: 24.9. 23.5, 19.3, 22.1, 20.4. 21.6, 21.3, 22.5. Assume that the two populations are normal. (a) (10 points) Find the sample variance; 3? and a: of the two samples. respectively. [b] (10 points) Find a 90% condence interval for the ratio of variances swag of the two populations. {c} [10 points) Use the 0.02 level of signicance to test whether it is reasonable to assume that the two samples come from populations with equal variance-3