Plant Operator Selection System Test Plant Operator Selection System Tables and Graphs Interpretation 3 — Questions and Answers
Question 1: An equipment maintenance log shows the following hours between failures for a compressor: 820, 950, 780, 1100, 870. What is the median time between failures?
- 870 hours (Correct answer)
- 904 hours
- 950 hours
- 780 hours
Correct answer: 870 hours
Arranged in order: 780, 820, 870, 950, 1100 — the middle value (median) is 870 hours.
Question 2: A control chart shows that acceptable pH levels range from 6.8 to 7.2. Hourly readings are: 7.0, 7.1, 7.3, 6.9, 7.0. Which reading is out of specification?
- 7.3 (Correct answer)
- 7.1
- 6.9
- 7.0
Correct answer: 7.3
A pH of 7.3 exceeds the upper control limit of 7.2 and falls outside the acceptable range.
Question 3: A graph shows steam pressure in Boiler A and Boiler B over 8 hours. Boiler A averages 120 psi and Boiler B averages 95 psi. What is the ratio of Boiler A's average pressure to Boiler B's?
- 24:19 (Correct answer)
- 6:5
- 5:4
- 12:9
Correct answer: 24:19
120:95 simplifies by dividing both by 5 to give 24:19.
Question 4: A table shows electricity consumption (kWh) by shift: Day=12,400, Evening=10,800, Night=9,600. The plant's daily energy budget is 34,000 kWh. By how much does actual usage differ from the budget?
- 1,200 kWh under budget (Correct answer)
- 1,200 kWh over budget
- 200 kWh under budget
- 800 kWh over budget
Correct answer: 1,200 kWh under budget
Total usage = 12,400 + 10,800 + 9,600 = 32,800 kWh, which is 34,000 − 32,800 = 1,200 kWh under budget.
Question 5: A scatter plot shows that as ambient temperature increases, cooling water demand also increases. This relationship is best described as:
- Positive correlation (Correct answer)
- Negative correlation
- No correlation
- Inverse proportion
Correct answer: Positive correlation
When both variables increase together, the scatter plot shows a positive correlation.
Question 6: A production table shows output per hour for 5 days: Mon=450, Tue=420, Wed=480, Thu=460, Fri=390. What is the range of hourly output?
- 90 units (Correct answer)
- 72 units
- 60 units
- 45 units
Correct answer: 90 units
Range = highest − lowest = 480 − 390 = 90 units.
Question 7: A stacked bar chart shows that Unit 1 produced 600 tons and Unit 2 produced 400 tons last month. This month Unit 1 produced 660 tons and Unit 2 produced 440 tons. What was the overall percentage increase in production?
- 10% (Correct answer)
- 8%
- 12%
- 6%
Correct answer: 10%
Last month total = 1,000 tons; this month = 1,100 tons; increase = 100/1,000 × 100 = 10%.
Plant Operator Selection System Test Plant Operator Selection System Tables and Graphs Interpretation 3
An equipment maintenance log shows the following hours between failures for a compressor: 820, 950, 780, 1100, 870.
What is the median time between failures?