In systematic sampling, a list of 1,200 students is available, and a sample of 100 is needed. The sampling interval is 12. If the random start is number 7, which of the following is NOT selected?
- A 7
- B 25 ✓
- C 19
- D 31
Correct answer: B. 25
Explanation
In systematic sampling with interval 12 and start 7, selected individuals are: 7, 19, 31, 43, 55... The sequence follows 7 + (n×12). Number 25 = 7 + 18, which is not a multiple of 12 from start 7 (7+12=19, 7+24=31); therefore 25 is not selected. This tests understanding of the systematic sampling progression.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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