A worker-machine operation was found to involve 3.3 minutes of machine time per cycle in the course of 40 cycles of stopwatch study. The worker’s time averaged 1.9 minutes per cycle, and the worker was given a rating of 120 percent (machine rating is 100 percent). Midway through the study, the worker took a 10-minute rest break. Assuming an allowance factor of 12 percent of work time, determine the standard time for this job.
The Correct Answer and Explanation is :
To calculate the standard time for this job, we can use the following formula:
[
\text{Standard Time} = \left( \text{Observed Time} \times \text{Rating Factor} \right) + \text{Allowance}
]
Step 1: Calculate the Observed Time
The observed time is the average time per cycle recorded for the worker, which is 1.9 minutes per cycle.
Since the worker worked for 40 cycles, the total observed time is:
[
\text{Total Observed Time} = 1.9 \, \text{minutes per cycle} \times 40 \, \text{cycles} = 76 \, \text{minutes}
]
Step 2: Apply the Rating Factor
The worker is rated at 120%, or 1.2 as a factor. So, the rated time per cycle is:
[
\text{Rated Time per Cycle} = 1.9 \times 1.2 = 2.28 \, \text{minutes per cycle}
]
For all 40 cycles:
[
\text{Total Rated Time} = 2.28 \, \text{minutes per cycle} \times 40 = 91.2 \, \text{minutes}
]
Step 3: Add the Machine Time
The machine time per cycle is 3.3 minutes. For all 40 cycles:
[
\text{Total Machine Time} = 3.3 \times 40 = 132 \, \text{minutes}
]
Step 4: Add the Rest Break
The worker took a 10-minute rest break, so we add this break time to the total:
[
\text{Total Time Including Rest} = 91.2 + 132 + 10 = 233.2 \, \text{minutes}
]
Step 5: Apply the Allowance Factor
The allowance factor is 12%, so the total allowance is:
[
\text{Allowance} = 0.12 \times 233.2 = 27.98 \, \text{minutes}
]
Step 6: Calculate the Standard Time
The standard time is the total time (including machine time and worker time) plus the allowance:
[
\text{Standard Time} = 233.2 + 27.98 = 261.18 \, \text{minutes}
]
Thus, the standard time for this job is 261.18 minutes.
Explanation
The standard time calculation is used to determine the expected time it should take for a worker to complete a job under normal working conditions. This time accounts for both the observed work time, the machine time, and any allowances (breaks, delays, or other necessary activities). By adding the 12% allowance for rest and fatigue, we ensure the standard time reflects the total time required under realistic conditions. The rating factor adjusts the worker’s actual performance to reflect their efficiency, and the observed time is adjusted accordingly.