All solutions here are SUGGESTED. Mr. Teng will hold no liability for any errors. Comments are entirely personal opinions.
(i)
interval = 
Order the list of 10000 regular customers, then randomly select a number from 1 to 20, e.g. 4. Then select the 4th, 24th, 44th, 64th, … customers on the list until all 500 customers are surveyed.
(ii)
Advantage:
1. Sample is evenly spread out over the list of customers.
Disadvantage:
1. Not representative as the list could exhibit periodic or cyclic pattern.
2. Biased as the list could exhibit periodic or cyclic pattern.
Personal Comments:
Students, please go memorise how to describe these methods and know how to write in context. We MUST write in context of the question.
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