In computing descriptive statistics from grouped data, a. data values are treated as if they occur at the midpoint of a class. b. the grouped data result is more accurate than the ungrouped result. c. the grouped data computations are used only when a population is being analyzed. d. none of these alternatives is correct.

Match the steps of the process to julia's analysis. 1. analyze choices. current costs for making phone calls to foreign countries averages between five and ten cents a minute. 2. determine the goals. julia needs to reduce the cost of telecommunications without reducing her employees' ability to do their jobs. 3. gather data. the corporate computer network will be able to handle the increased traffic that will occur as a result of voip. 4. evaluate the decision. julia will have her it department set up voip in the smallest domestic office. 5. make the decision. julia will have employees document the benefits and problems that result from using the new technology.

Consider a slotted aloha system, where the time slot equals the fixed duration of each packet. assume that there are 4 stations a,b,c,d sharing the medium. (a) stations a,b,c,d receive one packet each from higher layers at times 1.3, 1.5, 2.6,5.7 respectively. show which transmissions take place when, according to the slottedaloha protocol; describe all transmissions until all four packets have been successful.when needed, each station has access to the following sequence of random number, provided by a random number generator and drawn uniformly between 0 and 1: (1) station a draws numbers: 0.31, 0.27, 0.78, 0.9, 0.9, 0.11, 0. (2) station b draws numbers: 0.45, 0.28, 0.11, 0.83, 0.37, 0.22, 0. (3)station c draws numbers: 0.1, 0.2, 0.3, 0.4, 0. (4) station d draws numbers: 0.36, 0.77, 0.9, 0.1, 0.1, 0.1, 0.1, 0. (b) in slotted aloha, a station transmits in each time slot with a given probability. what probabilities would you assign to each of the four stations so as to: (i) maximize the efficiency of the protocol? (ii) maximize fairness among the four stations? (c) will the efficiency increase or decrease if we modify slotted aloha as follows: (i) get rid of slots and allow stations to transmit immediately? (ii) implement carrier sensing? (iii) implement collision detection? (iv) implement collision avoidance?

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