Kirsten Cookie Case

Solution to Kristen's Cookie Company (A)

Before answering specific questions, it is useful to make a diagram of the overall process:

Note that in this diagram, activities are arranged in columns to indicate which resources are being used. Inside each activity symbol are written the capacity (in dozens of cookies) and the cycle time (in minutes).

1. How long will it take for you to fill a rush order?

Assuming this order is for one dozen cookies, we will need to do the following:

Activity Resource Cycle Time Start Time Finish Time

Order Entry E-mail 0 minutes 00:00 00:00

Wash Bowl, Mix Self 6 minutes 00:00 06:00

Fill Tray Self 2 minutes 06:00 08:00

Prepare Oven Roommate 1 minute 08:00 09:00

Bake Oven 9 minutes 09:00 18:00

Remove Roommate 0 minutes 18:00 18:00

Cool None 5 minutes 18:00 23:00

Pack, Collect Money Roommate 3 minutes 23:00 26:00

Therefore, the minimum time to fill an order is 26 minutes. We can illustrate the sequence of events with a Gantt chart:

2. How many orders can you fill in a night, assuming you are open four hours each night?

Here is a Gantt chart for two batches of one dozen cookies each. It doesn't take twice as long to produce two batches as it does to produce one batch, because you can start mixing the second batch without having to wait for the whole first-batch process to be completed (you can start washing out the bowl as soon as you finish filling the tray). It is possible to produce two batches in 36 minutes.

In general, a formula for the number of minutes to produce n one-dozen batches is given by this expression:

3. How much of your own and your roommate's valuable time will it take to fill each order?

For yourself:

Activity Cycle Time

Wash Bowl, Mix 6 minutes

Fill Tray 2 minutes

Total 8 minutes

For your roommate:

Activity Cycle Time

Prepare Oven 1 minute

Remove 0 minutes

Pack, Collect Money 3 minutes

Total 4 minutes

This is assuming all orders are for one dozen cookies.

4. Because your baking trays can hold exactly one dozen cookies, you will produce and sell cookies by the dozen. Should you give any discount for people who order two dozen cookies, three dozen cookies, or more? If so, how much? Will it take any longer to fill a two-dozen cookie order than a one-dozen cookie order?

First, let's consider costs. The cost of ingredients and the box are the same, no matter how many dozen you bake. So the only resource that might differ with the size of the batch is labor.

One Dozen

Activity Resource Cycle Time Start Time Finish Time

Order Entry E-mail 0 minutes 00:00 00:00

Wash Bowl, Mix Self 6 minutes 00:00 06:00

Fill Tray Self 2 minutes 06:00 08:00

Prepare Oven Roommate 1 minute 08:00 09:00

Bake Oven 9 minutes 09:00 18:00

Remove Roommate 0 minutes 18:00 18:00

Cool None 5 minutes 18:00 23:00

Pack, Collect Money Roommate 3 minutes 23:00 26:00

Self 8

Roommate 4

Total Labor Minutes 12

Two Dozen

Activity Resource Cycle Time Start Time Finish Time

Order Entry E-mail 0 minutes 00:00 00:00

Wash Bowl, Mix Self 6 minutes 00:00 06:00

Fill Tray 1 Self 2 minutes 06:00 08:00

Fill Tray 2 Self 2 minutes 08:00 10:00

Prepare Oven 1 Roommate 1 minute 08:00 09:00

Bake 1 Oven 9 minutes 09:00 18:00

Remove 1 Roommate 0 minutes 18:00 18:00

Cool 1 None 5 minutes 18:00 23:00

Prepare Oven 2 Roommate 1 minute 18:00 19:00

Bake 2 Oven 9 minutes 19:00 28:00

Remove 2 Roommate 0 minutes 28:00 28:00

Cool 2 None 5 minutes 28:00 33:00

Pack 1 Roommate 2 minutes 23:00 25:00

Pack 2 Roommate 2 minutes 33:00 35:00

Collect Money Roommate 1 minute 35:00 36:00

Self 10

Roommate 7

Total Labor Minutes 17

Three Dozen

Activity Resource Cycle Time Start Time Finish Time

Order Entry E-mail 0 minutes 00:00 00:00

Wash Bowl, Mix Self 6 minutes 00:00 06:00

Fill Tray 1 Self 2 minutes 06:00 08:00

Fill Tray 2 Self 2 minutes 08:00 10:00

Fill Tray 3 Self 2 minutes 06:00 08:00

Prepare Oven 1 Roommate 1 minute 08:00 09:00

Bake 1 Oven 9 minutes 09:00 18:00

Remove 1 Roommate 0 minutes 18:00 18:00

Cool 1 None 5 minutes 18:00 23:00

Prepare

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