The average flow time for the jobs listed in the table below under the longest processing time (LPT)rule is ______. $$\begin{array} { | c | c | c | }
\hline \text { Job } & \begin{array} { c }
\text { Processing time } \
\text { (in days\} }
\end{array} & \begin{array} { c }
\text { Due date (in days from } \
\text { today's date\} }
\end{array} \
\hline \text { A } & 4 & 9 \
\hline \text { B } & 10 & 18 \
\hline \text { C } & 6 & 6 \
\hline \text { D } & 12 & 19 \
\hline \text { E } & 7 & 17 \
\hline
\end{array}$$
A)27.4 days
B)24.4 days
C)23.4 days
D)26.7 days

Question

The average flow time for the jobs listed in the table below under the longest processing time (LPT)rule is ______. $$\begin{array} { | c | c | c | } 
\hline \text { Job } & \begin{array} { c } 
\text { Processing time } \
\text { (in days\} }
\end{array} & \begin{array} { c } 
\text { Due date (in days from } \
\text { today's date\} }
\end{array} \
\hline \text { A } & 4 & 9 \
\hline \text { B } & 10 & 18 \
\hline \text { C } & 6 & 6 \
\hline \text { D } & 12 & 19 \
\hline \text { E } & 7 & 17 \
\hline
\end{array}$$
A)27.4 days
B)24.4 days
C)23.4 days
D)26.7 days

Quizplus · Accepted Answer

LPT rule means that the job with the longest processing time is scheduled first. So, the order of the jobs is D, B, E, A, C. The flow time for each job is the sum of its processing time and the waiting time. The waiting time for a job is the sum of the processing times of all the jobs that precede it. So, the flow time for job D is 12 days, the flow time for job B is 12 + 10 = 22 days, the flow time for job E is 22 + 7 = 29 days, the flow time for job A is 29 + 4 = 33 days, and the flow time for job C is 33 + 6 = 39 days. The average flow time is (12 + 22 + 29 + 33 + 39) / 5 = 27.4 days.

The Average Flow Time for the Jobs Listed in the Table