9.5.1. The waiting time in milliseconds, W, for accessing one record from a computer database is the continuous uniform (0,10) random variable. The read time R (for moving the information from the disk to main memory) is 3 milliseconds. The random variable X milliseconds is the total access time (waiting time +read time) to get one block of information from the disk. Before performing a certain task, the computer must access 12 different blocks of information from the disk. (Access times for dif- ferent blocks are independent of one another.) The total access time for all the information is a ran- dom variable A milliseconds. (a) What is E[X]? (b) What is Var[X]? (c) What is E[A]? (d) What is oĄ? time? (e) Use the central limit theorem to estimate P[A > 116ms]. (f) Use the central limit theorem to estimate P[A < 86ms].

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Solve part (a), (b), (c)

9.5.1. The waiting time in milliseconds, W, for accessing one record from a computer database is the
continuous uniform (0,10) random variable. The read time R (for moving the information from the
disk to main memory) is 3 milliseconds. The random variable X milliseconds is the total access time
(waiting time +read time) to get one block of information from the disk. Before performing a certain
task, the computer must access 12 different blocks of information from the disk. (Access times for dif-
ferent blocks are independent of one another.) The total access time for all the information is a ran-
dom variable A milliseconds.
(a) What is E[X]?
(b) What is Var[X]?
(c) What is E[A]?
(d) What is oĄ? time?
(e) Use the central limit theorem to estimate P[A > 116ms].
(f) Use the central limit theorem to estimate P[A < 86ms].
Transcribed Image Text:9.5.1. The waiting time in milliseconds, W, for accessing one record from a computer database is the continuous uniform (0,10) random variable. The read time R (for moving the information from the disk to main memory) is 3 milliseconds. The random variable X milliseconds is the total access time (waiting time +read time) to get one block of information from the disk. Before performing a certain task, the computer must access 12 different blocks of information from the disk. (Access times for dif- ferent blocks are independent of one another.) The total access time for all the information is a ran- dom variable A milliseconds. (a) What is E[X]? (b) What is Var[X]? (c) What is E[A]? (d) What is oĄ? time? (e) Use the central limit theorem to estimate P[A > 116ms]. (f) Use the central limit theorem to estimate P[A < 86ms].
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