A tricky combinations problem??

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A tricky combinations problem??

by RACHVIK » Sat Jan 01, 2011 1:38 am
A rectangular floor measures 2 by 3 meters. There are 5 white, 5 black, and 5 red parquet blocks available. If each block measures 1 by 1 meter, in how many different color patterns can the floor be parqueted?

* 104
* 213
* 577
* 705
* 726

Some expert pls help!!
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by Anurag@Gurome » Sat Jan 01, 2011 4:28 am
RACHVIK wrote:A rectangular floor measures 2 by 3 meters. There are 5 white, 5 black, and 5 red parquet blocks available. If each block measures 1 by 1 meter, in how many different color patterns can the floor be parqueted?

* 104
* 213
* 577
* 705
* 726
The rectangular floor measures 2 by 3 meters.
Thus there are 2*3 = 6 blocks of measurement 1 by 1 meter.

Now there are 3 possible color for each block.
Thus if we had infinite numbers of parquet blocks of each color, we would've done the decoration in 3^6 = 729 ways.

But we have a limited number of parquet blocks of each color, i.e 5 of each. Therefore all of the blocks cannot be of the same color at the same time. Thus all of the 6 blocks are white or black or red is not possible. Therefore except these 3 impossible cases the scenario is same as if we have infinite numbers of parquet blocks.

Therefore, actual number of different patterns = (729 - 3) = 726

The correct answer is E.
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by GMATGuruNY » Sat Jan 01, 2011 4:30 am
RACHVIK wrote:A rectangular floor measures 2 by 3 meters. There are 5 white, 5 black, and 5 red parquet blocks available. If each block measures 1 by 1 meter, in how many different color patterns can the floor be parqueted?

* 104
* 213
* 577
* 705
* 726

Some expert pls help!!
Floor area = b*h = 2*3 = 6 sq. meters.
Block area = b*h = 1*1 = 1 sq. meters.
Total number of blocks = Floor area/Block area = 6/1 = 6 blocks.

Good combinations = Total possible combinations - Bad combinations

Total possible combinations:
For each block, we have 3 choices: white, black, or red.
Multiplying the number of choices we have for each of the 6 blocks, we get 3*3*3*3*3*3 = 729 possible combinations.

Bad combinations:
Since we have only 5 of each color, all 6 blocks cannot be of the same color. Thus, there are 3 bad combinations: all white, all black, all red.

Good combinations = Total - Bad = 729-3 = 726.

The correct answer is E.
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