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# One-fifth of the light switches produced by a certain

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Manager
Joined: 11 May 2007
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One-fifth of the light switches produced by a certain [#permalink]

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28 Nov 2007, 13:37
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?
(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

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CEO
Joined: 29 Mar 2007
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28 Nov 2007, 16:02
yogachgolf wrote:
One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?
(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

I think something is missing here.

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Senior Manager
Joined: 09 Oct 2007
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28 Nov 2007, 18:33
haha, I agree. I tried reading a few times. I was thinking: where's the trick?

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Manager
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28 Nov 2007, 19:44
GMATBLACKBELT wrote:
yogachgolf wrote:
One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?
(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

I think something is missing here.

The wording is certainly not as good as OG. For practice, what part do you think is missing from the question?

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CEO
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28 Nov 2007, 20:03
yogachgolf wrote:
GMATBLACKBELT wrote:
yogachgolf wrote:
One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?
(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

I think something is missing here.

The wording is certainly not as good as OG. For practice, what part do you think is missing from the question?

Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake.

and what of nondefective switches??? 4/5's? this is really ambigious here it seems to be missing something

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Senior Manager
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28 Nov 2007, 22:25
Yeah. I still agree. With the given info I would say 16% (4/5 of 1/5), but wording of the problem makes me believe there's more...

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SVP
Joined: 04 May 2006
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28 Nov 2007, 22:45
I think the nonrejected can not be calculated due to lack of infomation "Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake" is not clea

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Intern
Joined: 28 Nov 2007
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28 Nov 2007, 23:10
yogachgolf wrote:
One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?
(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

where'd you get this question from

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Manager
Joined: 11 May 2007
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29 Nov 2007, 08:44
sondenso wrote:
I think the nonrejected can not be calculated due to lack of infomation "Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake" is not clea

Copy/paste error...the question should be:
One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and 1/20 of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective?
(A) 4%
(B) 5%
(C) 6.25%
(D) 11%
(E) 16%

I did the question again and found the answer by using matrix. This question is from the 1000 series.

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Manager
Joined: 20 Jun 2007
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29 Nov 2007, 09:10
Say 100 are produced
Of these 20 are defective (1/5)
Of these 16 are rejected (4/5)
and 4 sold

Of the 100, 80 are okay
Of these 4 are rejected (1/20)
and 76 sold

So 80 are sold (4 + 76)
of which 4 are defective.

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CEO
Joined: 29 Mar 2007
Posts: 2554

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29 Nov 2007, 09:26
Raffie wrote:
Say 100 are produced
Of these 20 are defective (1/5)
Of these 16 are rejected (4/5)
and 4 sold

Of the 100, 80 are okay
Of these 4 are rejected (1/20)
and 76 sold

So 80 are sold (4 + 76)
of which 4 are defective.

Same approach. nice!

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29 Nov 2007, 09:26
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