Of all the houses on Kermit Lane, 20 have front porches, 20 have front yards, and 40 have back yards. How many houses are on Kermit Lane?
(1) No house on Kermit Lane is without a back yard.

(2) Each house on Kermit Lane that has a front porch does not have a front yard.

How do I know this is an overlapping set of 3 sets? ok, I went straight to statement 1 and I thought t hen the answer would be 40.
same with Statement 2, I thought the ans is d

Ans is A
thanks,

The language here is "Of all the houses on Kermit Lane, 20 have front porches, 20 have front yards, and 40 have back yards." That means (without looking at the statements and letting them bias us!) that we can have houses with:

Front porches (FP) and Front yards (FY) and Back yards (BY)
FP and FY
FP and BY
FY and BY
just FY
just FP
just BY

My point here is not that you should write out these possibilities--just recognize that there is nothing in the wording of the sentence to tell us that any of these combinations couldn't exist. The other sign that this could be a 3-way overlapping set is that there are 3 qualities listed, none of which prevents the others from existing. (If you have a backyard, having a front yard is still possible. In contrast, being a college graduate automatically means that one is not a preschool student.)