A rectangular tiled floor consists of 70 square tiles.

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M7MBA: Moderator; Posts: 2058; Joined: Sun Oct 29, 2017 4:24 amFollowed by: 5 members; Thanked: 1 times

by M7MBA » Sat Mar 31, 2018 8:06 am

A rectangular tiled floor consists of 70 square tiles. The rectangular floor is being rearranged so that 2 tiles will be removed from each row of tiles and 4 more rows of tiles will be added. After the change in layout, the floor will still have 70 tiles, and it will still be a rectangle. How many rows were in the tile floor before the change in layout?

A) 4
B) 7
C) 10
D) 14
E) 28

The OA is C.

How can I solve this PS question? I tried but I couldn't. Help.!!

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Source: Beat The GMAT — Problem Solving | Sat Mar 31, 2018 8:06 am

swerve: Legendary Member; Posts: 2535; Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members

by swerve » Sat Mar 31, 2018 8:17 am

Hi M7MBA,

You can solve this PS question as follows,

A) 4
Before r = 4 then column 70/4 = remainder... no possible.

B) 7
Before r = 7 then column 70/7 = 10

After the 4 rows are added and 2 columns are removed
(7+4) * (10-2) != 70 wrong

C) 10
Before r = 10 column = 70/10 = 7
After the 4 rows are added and 2 columns are removed
(10+4)*(7-2) = 14*5 = 70 number of times ramained same

D) 14

E) 28

Hence, the correct answer is the option C.

Regards!

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ErikaPrepScholar: Legendary Member; Posts: 503; Joined: Thu Jul 20, 2017 9:03 amFollowed by: 15 members; Thanked: 86 times; GMAT Score:770

by ErikaPrepScholar » Sat Mar 31, 2018 11:33 am

You can also solve this problem by building equations.

A rectangular tiled floor consists of 70 square tiles. The rectangular floor is being rearranged so that 2 tiles will be removed from each row of tiles and 4 more rows of tiles will be added. After the change in layout, the floor will still have 70 tiles, and it will still be a rectangle. How many rows were in the tile floor before the change in layout?

Let's set
r = initial rows of tiles
t = initial tiles in each row
so
r*t = 70

Then we take away 2 from each row (t - 2) and add 4 rows (r + 4). We still have 70 tiles, so
(r+4)(t-2) = 70.
rt - 2r + 4t - 8 = 70

Plugging in 70 for rt and 70/r for t (rt = 70 --> t = 70/r):
70 - 2r + 4(70/r) - 8 = 70
2r - 280/r + 8 = 0
r - 140/r + 4 = 0
r^2 + 4r - 140 = 0
(r - 10)(r + 14) = 0
r = 10 ; r = -14

Since we can't have a negative number of rows, the original number of rows (r) must be 10.

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