Which job should I tackle first?
We all have times when there are just a stack of jobs to do and we have to decide which ones we’re going to tackle first. A knowledge of queueing theory can help us decide.
Suppose you have 5 jobs in the queue and each one will take a different amount of time –
Job 1 – 7 hours; Job 2 – 3 hours; Job 3 – 5 hours; Job 4 – 1 hour; Job 5 – 12 hours
If you do the longest job first, then the next longest and so on, doing the shortest job last, then the waiting times are –
|Job 5||Job 1||Job 3||Job 2||Job 4||Total|
|Job time||12||7||5||3||1||28 hours|
|Waiting time||12||12 + 7 = 19||19 + 5 = 24||24 + 3 = 27||27 + 1 = 28||110 hours|
D’you see that the 1 hour job waited for 28 hours before it was finished?
Now, what if you do the quickest job first, then the next quickest and so on, doing the longest job last –
|Job 4||Job 2||Job 3||Job 1||Job 5||Total|
|Job time||1||3||5||7||12||28 hours|
|Waiting time||1||1 + 3 = 4||4 + 5 = 9||9 + 7 = 16||16 + 12 = 28||43 hours|
Notice that either way it will take you 28 hours to finish all jobs, but by doing the quickest job first you cut the total waiting time from 110 hours to 43!
So, all else being equal, tackle the quickest job first.
Of course, you have to take care that the longer jobs do get done, otherwise they will just keep sinking to the bottom of the In Box.