data sufficien, a hard and official one

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tanviet: Legendary Member; Posts: 1404; Joined: Tue May 20, 2008 6:55 pmFollowed by: 2 members; Thanked: 18 times

by tanviet » Thu Apr 16, 2009 2:53 am

Theater M has 25 rows with 27 seats in each row. How many of the seats were occupied during a certain show?

1, dering the show, there was an average (arithmetic men) of 10 unoccupied seats per row for the front 20 row

2, Dering the show, there was an average (arithmetic mean) of 20 unoccupied seats per row for th back 15 rows.

pls, help with this

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Source: Beat The GMAT — Data Sufficiency | Thu Apr 16, 2009 2:53 am

bluementor: Master | Next Rank: 500 Posts; Posts: 418; Joined: Wed Jun 11, 2008 5:29 am; Thanked: 65 times

by bluementor » Thu Apr 16, 2009 4:14 am

Statement 1: we don't know anything about the last 5 rows. Insufficient.

Statement 2: we don't know anything about the first 10 rows. Insufficient.

Both statements together:

the first 20 rows (rows 1-20) -> 20*10 seats unoccupied
the last 15 rows (rows 11-25) -> 15*20 seats unoccupied

we still need at least one of these to be able to answer the question stem:

a) the average of unoccupied seats from rows 1-10
b) the average of unoccupied seats from rows 11-20, or
c) the average of unoccupied seats from rows 21-25

Insufficient.

Choose E.

-BM-

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