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Difficulty: 505-555 Level,   Statistics and Sets Problems,                                    
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
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Abhishek009 wrote:
Walkabout wrote:
For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 90 units raises the average to 55 units per day, what is the value of n ?

(A) 30
(B) 18
(C) 10
(D) 9
(E) 7


\(\frac{50n + 90}{n + 1}= 55\)

\(50n + 90 = 55n + 55\)

\(5n = 45\)

So, \(n = 9\)

Thus, answer must be (D) 9



\(55(n+1)-50n=90\)

\(⇒ 55n+55-50n=90\)

\(⇒ 5n=35\)

\(∴ n=7\)

The answer E, Do you may have a typo.
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
Top Contributor
Walkabout wrote:
For the past n days, the average (arithmetic mean) daily production at a company was 50 units. If today's production of 90 units raises the average to 55 units per day, what is the value of n ?

(A) 30
(B) 18
(C) 10
(D) 9
(E) 7



The average is 50, the additional units have to be divided among the total people as the average increased.

The additional units beyond average 90-50=40

So, \(\frac{40}{n+1}=5\)
\(⇒ 5n+5=40\)
\(⇒ 5n=35\)
\(⇒n=7\)

The answer E.
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
avigutman wrote:
Video solution from Quant Reasoning:
Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1


avigutman

Thank you! Perhaps I am reading into this too much, but how do we necessarily know that there are not any days in between the "past n days" and today? What if there was break?
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
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woohoo921 wrote:
Perhaps I am reading into this too much, but how do we necessarily know that there are not any days in between the "past n days" and today? What if there was break?


Does this help, woohoo921?
https://www.gymglish.com/en/gymglish/en ... seven-days

Posted from my mobile device
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
avigutman wrote:
woohoo921 wrote:
Perhaps I am reading into this too much, but how do we necessarily know that there are not any days in between the "past n days" and today? What if there was break?


Does this help, woohoo921?
https://www.gymglish.com/en/gymglish/en ... seven-days

Posted from my mobile device


avigutman
Thank you for your quick response. As a general rule, when the GMAT says "past few days" does that just always mean a few days prior until now?
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
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Expert Reply
woohoo921 wrote:
avigutman wrote:
woohoo921 wrote:
Perhaps I am reading into this too much, but how do we necessarily know that there are not any days in between the "past n days" and today? What if there was break?


Does this help, woohoo921?
https://www.gymglish.com/en/gymglish/en ... seven-days

As a general rule, when the GMAT says "past few days" does that just always mean a few days prior until now?

Yes, woohoo921. And that rule isn't limited to the GMAT.
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Re: For the past n days, the average (arithmetic mean) daily [#permalink]
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