The plant manager wants to determine a standard time for welding operations, which vary greatly in terms of size/length per weld and other parameters. The manager estimates that about 30% of time currently is spent idle or on breaks, and the rest is on productive operations. You conduct a work sampling study to verify that percentage and to develop a standard time. 1. How many observations should you collect to have a 90% confidence level and +/- 5% accuracy in your results?
2. You end up with 168 observations of productive operations from 8 welders working 40-hour weeks over a period of 4 weeks. If 725 units were produced in this time, what is the average time per unit?
3. To determine a standard time, you estimate a performance rating of 97% for all workers and assume a PFD allowance of 22% after consulting with the plant manager. What is the standard time for 1 unit?
4. An order comes in for 150 units that must be finished in one week. How many welders should the plant manager allocate towards this order to meet the deadline?