I don't really understand this question.
A, B and D are clearly out. Consider C and E.
Take x as the number of houses which carry both types of tables.
From (1) we have: the number of houses with a ping-pong table = 20 + x
From (2) we have: the number of houses with a soccer table = 40 = x + the number of houses with a soccer table only.
From (1) and (2) we have: 20 + x + 40 - x = 50 unreasonable. Anyone can explain???
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