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Bulusuchaitanya
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Bulusuchaitanya
A rectangular floor is fully covered with square tiles of identical size. The tiles on the edges are white and the tiles in the interior are red. The number of white tiles is the same as the number of red tiles. A possible value of the number of tiles along one edge of the floor is :

(a) 10
(b) 12
(c) 14
(d) 16
(e) 18

Let the inner rectangle be in column and row x*y, so red tiles =xy
The white tiles=(x+2)*1*2+y*1*2)=2x+4+2y
So 2x+2y+4=xy.........
2x+4=xy-2y=y(x-2)..........
\(y=\frac{2x+4}{x-2}\)..
Now x will be 2 less than the value we are looking for and y should be an integer..
Let us see..
A) 10......X=8, so y=(2*8+4)/(8-2)=20/6...NO
B) 12.....x=10, so y=(2*10+4)/(10-2)=24/8=3....YES
C) 14....y=28/10...NO
D) 16...y=32/12...NO
E) 18....y=40/16...NO

B
Hi
I lost you here itself : Let the inner rectangle be in column and row x*y, so red tiles =xy
The white tiles=(x+2)*1*2+y*1*2)=2x+4+2y

Please elaborate

I have added a pic and attached a figure.
Since the tiles are square, I take y*X tiles of red colour placed in a rectangular form.
The outer layer will have one more on each side.
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Bunuel could you please explain this? Thank you
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LMP
A rectangular floor is fully covered with square tiles of identical size. The tiles on the edges are white and the tiles in the interior are red. The number of white tiles is the same as the number of red tiles. A possible value of the number of tiles along one edge of the floor is :

(a) 10
(b) 12
(c) 14
(d) 16
(e) 18

\(area: xy = white + red\)
\(white: 2(x+y)-corners=2(x+y)-4\)
\(red: xy-white=xy-(2(x+y)-4)=xy-2(x+y)+4\)
\(white=red…2(x+y)-4=xy-2(x+y)+4…4(x+y)-xy-8=0…4x+4y-xy-8=0\)
\((x,y)=intergers…4x+4y-xy-8=0…4x-xy=8-4y…x=(8-4y)/(4-y)=integer\)

\(y=10…(8-4y)/(4-y)=8-40/4-10=-32/-6≠integer\)
\(y=12…(8-4y)/(4-y)=8-48/4-12=-40/-8=integer\)
\(y=14…(8-4y)/(4-y)=8-4(14)/4-14≠integer\)
\(y=16…(8-4y)/(4-y)=8-4(16)/4-16≠integer\)
\(y=18…(8-4y)/(4-y)=8-4(18)/4-18≠integer\)

Answer (B)
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