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ketkoag: Legendary Member; Posts: 876; Joined: Thu Apr 10, 2008 8:14 am; Thanked: 13 times

by ketkoag » Sun Mar 29, 2009 5:54 am

Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a
certain show?
(1) During the show, there was an average (arithmetic mean) of 10 unoccupied
seats per row for the front 20 rows.
(2) During the show, there was an average (arithmetic mean) of 20 unoccupied seats per
row for the back 15 rows.

OA: E
How? If we take statement 1 then 10*20 seats are unoccupied. therefore rest all are occupied.
Now how we come to know that in the rest of the rows there is no empty seat.
Also we can assume that there are no unoccupied seats in the other rows if we consider statement 1.

Please help to understand the ambiguity..

Source: Beat The GMAT — Data Sufficiency | Sun Mar 29, 2009 5:54 am

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Sun Mar 29, 2009 7:23 am

we need to find occupied seats for the rows 1 to 25

stmnt 1 gives data for unoccupied seats for rows 1 to 20, so we can find occupied seats for rows 1 to 20 only. we have no info about rows 21 to 25.
not sufficient

stmnt 2 gives data for unoccupied seats for rows 10 to 25, so we can find occupied seats for rows 10 to 25 only. we have no info about rows 1 to 9
not sufficient

combining, we have info on occupied seats between rows 1 to 20 and rows 10 to 25. no info about rows 1 to 9.
not sufficient

hence E

ketkoag: Legendary Member; Posts: 876; Joined: Thu Apr 10, 2008 8:14 am; Thanked: 13 times

by ketkoag » Sun Mar 29, 2009 10:05 am

thanks for your reply. but
what if i consider that no seat is unoccupied in rows from 21 to 25.
Similarly i can consider for the 2nd statement.
please explain why i cannot consider the above stated things for this ques.

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Sun Mar 29, 2009 10:52 am

statement 1: we are given info only on rows 1 to 20 in statement. nothing is mentioned about 21 to 25. so we cant assume anything about rows 21 to 25. we need to strictly go by whatever information has been given

likewise for statement 2

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