Friday, November 28, 2008
Susan has invited her family to Thanksgiving Dinner. As her plates are not the best, Susan wants to buy new plates – one for each person at her Thanksgiving Dinner.
There’ll be a grandfather, a grandmother, two fathers, two mothers, four children, three grandchildren, one brother, two sisters, two sons, two daughters, one father-in-law, one mother-in-law and a daughter-in-law.
At least how many plates does Susan need to buy?
Correct answer, Susan needs at least 7 plates.
• The grandfather is also a father and a father-in-law.
• The grandmother is also a mother and a mother-in-law.
• The father is also his parents’ son (and child).
• The daughter-in-law is also a mother.
• The grandson is also a brother and his parents’ son (and child).
• The two granddaughters are also sisters and their parents’ daughters (and children).
So we have
• one grandfather
• one grandmother
• two fathers (grandfather, father)
• two mothers (grandmother, daughter-in-law)
• four children (father, grandson, 2 granddaughters)
• three grandchildren (grandson, 2 granddaughters)
• one brother (grandson)
• two sisters (2 granddaughters)
• two sons (father, grandson)
• one father-in-law (grandfather)
• one mother-in-law (grandmother)
• one daughter-in-law