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Illinois Furniture, Inc., produces all types of office furniture. The “Executive Secretary” is a chair that has been designed using ergonomics to provide comfort during long work hours. The chair sells for $130. There are 480 minutes available during the day, and the average daily demand has been 50 chairs. There are eight tasks:
a) Draw a precedence diagram of this operation.
b) What is the cycle time for this operation?
c) What is the theoretical minimum number of workstations?
d) Assign tasks to workstations.
e) What is the idle time per cycle?
f) How much total idle time is present in an 8-hour shift?
g) What is the efficiency of the assembly line, given your answer in (d)?
a)
To draw: The precedence diagram.
Answer to Problem 13P
Explanation of Solution
Given information:
| Task | Time (minutes) | Immediate predecessors |
| A | 4 | - |
| B | 7 | - |
| C | 6 | A, B |
| D | 5 | C |
| E | 6 | D |
| F | 7 | E |
| G | 8 | E |
| H | 6 | F, G |
| Total | 49 |
- The chair is sold for $130.
- Number of minutes available = 480 / day.
- Average daily demand is 50 chairs.
Precedence diagram:
b)
To determine: The cycle time.
Introduction:
Cycle time:
Cycle time is the total time taken to complete an unit of work from the beginning of the process to the end of the process.
Answer to Problem 13P
The cycle time is 9.6 minutes / unit.
Explanation of Solution
Given information:
| Task | Time (minutes) | Immediate predecessors |
| A | 4 | - |
| B | 7 | - |
| C | 6 | A, B |
| D | 5 | C |
| E | 6 | D |
| F | 7 | E |
| G | 8 | E |
| H | 6 | F, G |
| Total | 49 |
- The chair is sold for $130.
- Number of minutes available = 480 / day.
- Average daily demand is 50 chairs.
Formula to calculate cycle time:
Calculation of cycle time:
The cycle time is 9.6 minutes / unit.
c)
To determine: The theoretical minimum number of workstations.
Answer to Problem 13P
The theoretical minimum number of workstations is 6 workstations.
Explanation of Solution
Given information:
| Task | Time (minutes) | Immediate predecessors |
| A | 4 | - |
| B | 7 | - |
| C | 6 | A, B |
| D | 5 | C |
| E | 6 | D |
| F | 7 | E |
| G | 8 | E |
| H | 6 | F, G |
| Total | 49 |
- The chair is sold for $130.
- Number of minutes available = 480 / day.
- Average daily demand is 50 chairs.
Formula to calculate theoretical minimum number of workstations:
Calculation of theoretical minimum number of workstations:
The theoretical minimum number of workstations is 6 workstations.
d)
To assign: The different tasks to different workstations.
Explanation of Solution
Assignment of different tasks to different workstations:
Task A is assigned to station 1. Task B is assigned to station 2. Task C is assigned to station 3. Task D is assigned to station 4. Task E is assigned to station 5. Task G is assigned to station 6. Task F is assigned to station 7. Task H is assigned to station 8.
e)
To determine: The idle time per cycle.
Answer to Problem 13P
The idle time is 15 minutes / cycle.
Explanation of Solution
Given information:
| Task | Time (minutes) | Immediate predecessors |
| A | 4 | - |
| B | 7 | - |
| C | 6 | A, B |
| D | 5 | C |
| E | 6 | D |
| F | 7 | E |
| G | 8 | E |
| H | 6 | F, G |
| Total | 49 |
- The chair is sold for $130.
- Number of minutes available = 480 / day.
- Average daily demand is 50 chairs.
Calculation of idle time per cycle:
The idle time is 15 minutes / cycle.
f)
To determine: The total idle time present in an 8 hour shift.
Answer to Problem 13P
The total idle time present in an 8 hour shift is 15 hours.
Explanation of Solution
Given information:
| Task | Time (minutes) | Immediate predecessors |
| A | 4 | - |
| B | 7 | - |
| C | 6 | A, B |
| D | 5 | C |
| E | 6 | D |
| F | 7 | E |
| G | 8 | E |
| H | 6 | F, G |
| Total | 49 |
- The chair is sold for $130.
- Number of minutes available = 480 / day.
- Average daily demand is 50 chairs.
Calculation of total idle time present in an 8 hour shift:
There are 480 minutes available in a day. The longest operation time is 8 minutes. Therefore the number of cycles in a day is given by:
The total idle time is calculated by multiplying the number of cycles with the total idle time per cycle.
The total idle time present in an 8 hour shift is 15 hours.
g)
To determine: The efficiency.
Introduction:
Efficiency:
Efficiency is the measure of what is actually produced as opposed to what can be theoretically produced with the same amount of resources.
Answer to Problem 13P
The efficiency is 76.6%.
Explanation of Solution
Given information:
| Task | Time (minutes) | Immediate predecessors |
| A | 4 | - |
| B | 7 | - |
| C | 6 | A, B |
| D | 5 | C |
| E | 6 | D |
| F | 7 | E |
| G | 8 | E |
| H | 6 | F, G |
| Total | 49 |
- The chair is sold for $130.
- Number of minutes available = 480 / day.
- Average daily demand is 50 chairs.
Formula to calculate efficiency:
Calculation of efficiency:
The efficiency is 76.6%
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Chapter 9 Solutions
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