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# In a factory that produces computer circuit boards, 4.5

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In a factory that produces computer circuit boards, 4.5 [#permalink]  18 May 2010, 15:59
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In a factory that produces computer circuit boards, 4.5 percent of all boards produced are found to be defective and are repaired before being sold, but 10 percent of all defective boards are sold without being repaired. What percentage of boards produced in the factory are defective?

A. 4.5%
B. 5.0%
C. 6.0%
D. 10.0%
E. 14.5%
[Reveal] Spoiler: OA

Last edited by Bunuel on 12 Jun 2012, 13:31, edited 1 time in total.
Edited the question and added the OA.
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Re: In a factory that produces computer circuit boards [#permalink]  18 May 2010, 22:01
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Total Boards = X
Total Defective Boards = Y

Out of this Y "Defective" boards 10% "Escaped" (GIVEN) and 90% "Get caught and fixed"

We know that "Get Caught and fixed" = 4.5% of X. This implies

90% of Y = 4.5% of X.

(90/100) * Y = (4.5/100) * X ===> Y = 0.05 * X ===> 5% of X.

Hope this helps.

What is the OA? Is it B?
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Re: In a factory that produces computer circuit boards [#permalink]  19 May 2010, 03:53
Thanks vijay17,

the correct answer is indeed B.
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Re: In a factory that produces computer circuit boards [#permalink]  12 Jun 2012, 12:22
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Just for the sake of some intuition one should consider this:

That actual 4.5 percent figure that got fixed from the entire amount is equal to 90 percent that got fixed. The 4.5 percent here is adjusted to the 10 percent that gets escaped. So the 4.5 percent of all boards that are found to be defective already includes the adjustment that 10 percent escaped. So in other words after 10 percent escapes that figure is 4.5 percent of total boards. So we need to figure out what the original defective boards in percentage were.

As we know 10% escaped and wasn't caught,
We also know that when we originally found 4.5% of boards and fixed them before selling them
So that 4.5% was in reality only 90% of all defective board since we missed 10%
So, 90% of all defective boards = 4.5% of all boards

So, (10% of y + 4.5% of x) = total number of defective boards = y

Key word here "found"

Last edited by iNumbv on 18 Jun 2013, 13:40, edited 1 time in total.
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Re: In a factory that produces computer circuit boards [#permalink]  12 Jun 2012, 12:49
i think total cb and defective cb are not required because (X/Y)*(Y/total) is the answer where x is defective and not repaired and y is defective and total is total no of bulbs.
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Re: In a factory that produces computer circuit boards, 4.5 [#permalink]  17 Jun 2012, 16:26

X = all boards
4.5% * X = all boards that are DEFECTIVE and repaired before being sold

Y = all DEFECTIVE boards
100% all boards - 10% all DEFECTIVE boards that are NOT being repaired before being sold = 90%

90% * Y = all DEFECTIVE boards that are repaired before being sold

.9*Y = .045*X
Y = (.045/.9) * X
Y = .05
Y = 5%
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Re: In a factory that produces computer circuit boards, 4.5 [#permalink]  26 Aug 2013, 21:22
As 10% of all defective boards are sold without being repaired, (100 - 10)% = 90% of all defective boards are sold after being repaired

So, 90% of all defective boards = 4.5% of all boards
--> 100% of all defective boards = (4.5/90)*100% = 5% of all boards
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Re: In a factory that produces computer circuit boards, 4.5 [#permalink]  27 Aug 2013, 01:52
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perseverant wrote:
In a factory that produces computer circuit boards, 4.5 percent of all boards produced are found to be defective and are repaired before being sold, but 10 percent of all defective boards are sold without being repaired. What percentage of boards produced in the factory are defective?

A. 4.5%
B. 5.0%
C. 6.0%
D. 10.0%
E. 14.5%

1. 10% of defective boards are not repaired . Therefore 90% of defective boards are repaired
2. 90% of defective boards is equal to 4.5% of all boards produced
3 Total percentage of defective boards produced = 4.5/90 * 100 = 5%
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Re: In a factory that produces computer circuit boards, 4.5 [#permalink]  07 Feb 2014, 06:05
T - total boards
D - ALL defective boards.

$$\frac{90}{100}*D=\frac{4.5}{100}* T$$

D = 5% of Total.

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Re: In a factory that produces computer circuit boards, 4.5 [#permalink]  12 Feb 2014, 13:17
SravnaTestPrep wrote:
perseverant wrote:
In a factory that produces computer circuit boards, 4.5 percent of all boards produced are found to be defective and are repaired before being sold, but 10 percent of all defective boards are sold without being repaired. What percentage of boards produced in the factory are defective?

A. 4.5%
B. 5.0%
C. 6.0%
D. 10.0%
E. 14.5%

1. 10% of defective boards are not repaired . Therefore 90% of defective boards are repaired
2. 90% of defective boards is equal to 4.5% of all boards produced
3 Total percentage of defective boards produced = 4.5/90 * 100 = 5%

Or similarly one can use smart numbers:

Let's say total produced were 1000

So we have that 45 were defective and repaired
Since 10% were not repaired, 90% of boards were defective and repaired
The 9/10x = 45, where 'x' is the total number of defective boards.

x = 50

Therefore percentage defective 50/1000 = 5%

Hope this clarifies
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Re: In a factory that produces computer circuit boards, 4.5 [#permalink]  19 Mar 2015, 23:54
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Re: In a factory that produces computer circuit boards, 4.5   [#permalink] 19 Mar 2015, 23:54
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