Frequently, natural process times are made up of several distinct stages. For instance, a

manual task can be thought of as being comprised of individual motions (or "therbligs" as

Gilbreth termed them).

Suppose a manual task takes a single operator an average of 1 hour to perform.

Alternatively, the task could be separated into 10 distinct 6-minute subtasks performed by

separate operators. Suppose that the subtask times are independent (i.e., uncorrelated), and

assume that the coefficient of variation is 0.75 for both the single large task and the small

subtasks. Such an assumption will be valid if the relative shapes of the process time

distributions for both large and small tasks are the same. (Recall that the variances of

independent random variables are additive.)

(a) What is the coefficient of variation for the 10 subtasks taken together?

(b) Write the expression relating the SCV of the original tasks to the SCV of the combined

task.

(c) What are the issues that must be considered before dividing a task into smaller

subtasks? Why not divide it into as many as possible? Give several pros and cons.

(d) One of the principles of JIT is to standardize production. How does this explain some of

the success of JIT in terms of variability reduction?