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I made this mistake while solving a ques.Throw some light?

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tejal777
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I made this mistake while solving a ques.Throw some light? [#permalink] New post   19 Jul 2009, 20:01
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Guys I was solving a question and I made this silly mistake.I corrected myself but was hoping somebody throw some light on where my concept was wrong.

Suppose 2/3 out of N employees dring regular coffee.Out of these 2/5 add cream.How many of the employees who drink regular coffee do not add cream?
Ans: 2/3n - 2/5n = 4n/15.(ans.)

What I did was:If 2/5 add cream,then 3/5 do not add cream.So 3/5 x 2/3n = 2/5n :(



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Re: I made this mistake while solving a ques.Throw some light? [#permalink] New post   19 Jul 2009, 22:23
tejal777 wrote:
Guys I was solving a question and I made this silly mistake.I corrected myself but was hoping somebody throw some light on where my concept was wrong.

Suppose 2/3 out of N employees dring regular coffee.Out of these 2/5 add cream.How many of the employees who drink regular coffee do not add cream?
Ans: 2/3n - 2/5n = 4n/15.(ans.)

What I did was:If 2/5 add cream,then 3/5 do not add cream.So 3/5 x 2/3n = 2/5n :(


Catch some light. :evil: Sorry, can't help ! :lol:


When you say 2/3 employees of total. It is \(2N/3\).

When you calculated 3/5 = do not add cream. It means \(3N/5\) do not add cream. It's \(3/5\) of total employees & not \(3/5\) of 'the employees who drink regular coffee'.

Let's say \(Y = 2N/3\) = employees who drink regular coffee.

You are supposed to multiply \(3/5\) to 'N' not to Y.

P.S. You can draw a venn diagram, if you are still confused. I am too lazy to draw one on Monday morning. :yawn:
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Re: I made this mistake while solving a ques.Throw some light? [#permalink] New post   19 Jul 2009, 23:09
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"Suppose 2/3 out of N employees dring regular coffee." => 2/3 drink regular coffee
"Out of these 2/5 add cream." of those who drink regular coffee (2/3), 2/5 add cream and 3/5 do not add cream. Hense of all employees 2/3 * 2/5 drink regular coffee and add cream, 2/3 * 3/5 drink regular coffea and dont add cream

"How many of the employees who drink regular coffee do not add cream?"
Answer should be 3/5. No need for multiplcation because we care about only employees who drink regular coffee.
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Re: I made this mistake while solving a ques.Throw some light? [#permalink] New post   19 Jul 2009, 23:16
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Welcome to GMAT Club PussInBoots!

I could not pass those "puppy" eyes. Ask anything you want :-D
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Re: I made this mistake while solving a ques.Throw some light? [#permalink] New post   19 Jul 2009, 23:21
bb wrote:
Welcome to GMAT Club PussInBoots!

I could not pass those "puppy" eyes. Ask anything you want :-D


Can I have that V42 of yours? :)
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Re: I made this mistake while solving a ques.Throw some light? [#permalink] New post   19 Jul 2009, 23:24
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PussInBoots wrote:
bb wrote:
Welcome to GMAT Club PussInBoots!

I could not pass those "puppy" eyes. Ask anything you want :-D


Can I have that V42 of yours? :)


Yep - It is buried somewhere here: new-to-the-verbal-forum-please-read-this-first-77546.html
:wink:
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Re: I made this mistake while solving a ques.Throw some light? [#permalink] New post   20 Jul 2009, 03:19
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Suppose 2/3 out of N employees dring regular coffee.Out of these 2/5 add cream.How many of the employees who drink regular coffee do not add cream?


Consider a number which is multiple of LCM of 3,5 ( Denominators of fraction in question) say 30.

2/3 of N i.e. 2/3 of 30 go for regular coffee. : 20 .
Out of these(20) 2/5 add cream: 8.

How many who drink do not add cream/ Total coffee drinkers: 20-8: 12/20 = 3/5*N



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Re: I made this mistake while solving a ques.Throw some light? [#permalink]
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