DS question

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DS question

by dunkin77 » Sat Jun 09, 2007 2:16 am
Hi,

OA is B -- Can anyone show me how to get the number of community that have swimming pool?

Thanks!
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by jayhawk2001 » Sat Jun 09, 2007 8:29 am
There are 2 ways you can count the total number of houses in the
community.

(i) 75 = P + S - PS + no-P-no-S.
P = Number of houses with pool, S = num houses with swimming pool
etc. Here, we subtract the number of homes with P&S as we have
already counted them in P and S.


(ii) 75 = Ponly + Sonly + PS + no-P-no-S
Here we add PS because we have not double counted homes.

Now, coming to the question, we know

75 = 48 + S - PS + no-P-no-S

1 - insufficient. Use the second formula. We can only get
75 = 38 + Sonly + PS + no-P-no-S. We have too many unknowns.

2 - sufficient. Use first formula. PS = no-P-no-S.
So, 75 = 48 + S. We can hence solve for S.

Hence B