For four persons, you'd need approximately four cups or 30 oz of mashed potatoes.
One serving of mashed potatoes is roughly one cup or 7 ounces.
To count the total amount, we have to multiply the serving size by the number of people eating.
Total amount = serving × persons = 1 cup × 4 = 4 cups
Or, if we go by weight:
Total amount = 7 oz × 4 persons = 28-30 oz.
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