Assignment:
Problem 1: Demand Uncertainty
You own two gas stations that have different levels of demand. Below are the gallons of gas each station has sold over the last 6 weeks. Week Water St Brown Deer Rd
7/21 9,623 3,629
7/28 8,126 4,252
8/4 12,129 2,982
8/11 11,236 4,295
8/18 9,174 5,026
8/25 9,582 4,908
a) Determine the average and standard deviation of demand for gas for each station. You may use Excel, but you must show the data and Excel formulas you used
b) Calculate the coefficient of variation for each station and state which station has the most predictable demand
Problem 2: Line Balancing
Employees at ABC Assembly Line work from 6am to 2pm Monday through Friday. Everyone on the assembly line is allowed a 30 minute lunch and two 15 minute breaks. Other cross-trained associates cover lunches and breaks for the associates on the assembly line so the line doesn't stop. On your second week at ABC Assembly Line, you record the processes of the assembly line are laid out in the following manner:
Task Predecessor
1 none
2 1
3 none
4 2
5 3
6 4, 5
The intern the summer before recorded the following observations:
Task 1 average cycle time = 1.1 min
Task 2 average cycle time = 0.8 min
Task 5 average cycle time = 1.4 min
You complete the 20 observations at each of the other 3 stations and record the following:
Task 3 average cycle time = 52 sec
Task 4 average cycle time = 36 sec
Task 6 average cycle time = 63 sec
Due to quality issues in the field causing $300k worth of parts to be recalled, a new quality check Task 4a needs to be added after Task 4 and the quality check must be completed before Task 6 can begin. The Quality Assurance Team estimates this new process will take an average of 27 seconds to complete. Prior to adding this quality check task, the line was achieving an output of 300 units per day and the Plant Manager needs to maintain that output.
Assuming the new quality check task is added, do the following:
a) Draw the precedence diagram with the processing times for each task displayed
b) Compute the Takt time for the line
c) Assign tasks to work stations using the greatest amount of time remaining as a heuristic rule
d) Compute the efficiency and percent idle time for the system
e) Determine which work station has the least amount of idle time . Determine which work station has the greatest amount of idle time .
Problem 3: Forecasting
Given these sales figures over the first 6 months of the year, your boss needs you to create a forecast model that can be used for the last 6 months of the year. Use three different forecasting methods (last period, 2 period moving average and 3 period moving average) to determine which would be best for forecasting the next 6 months. For your measure of "best", recommend to your boss the method with the lowest mean absolute deviation (MAD). What is your forecast for July?
Jan Feb Mar Apr May Jun
Units Sold 25 42 33 38 22 34
a) Calculate the MAD for each of the 3 forecasts
b) Provide your July forecast