For the past n days, the average (arithmetic mean) daily : GMAT Problem Solving (PS)
Check GMAT Club App Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 07 Dec 2016, 18:14

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# For the past n days, the average (arithmetic mean) daily

Author Message
TAGS:

### Hide Tags

Manager
Joined: 02 Dec 2012
Posts: 178
Followers: 5

Kudos [?]: 2206 [2] , given: 0

For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

27 Dec 2012, 05:28
2
KUDOS
10
This post was
BOOKMARKED
00:00

Difficulty:

15% (low)

Question Stats:

72% (02:46) correct 28% (01:26) wrong based on 762 sessions

### HideShow timer Statistics

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
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 35912
Followers: 6851

Kudos [?]: 90029 [0], given: 10402

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

27 Dec 2012, 05:29
Expert's post
1
This post was
BOOKMARKED
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

(average production for n days) * n = (total production for n days) --> 50n=(total production for n days);
(total production for n days) + 90 = (average production for n+1 days) * (n+1) --> 50n + 90 = 55 * (n+1) --> n=7.

Or as 40 extra units increased the average for n+1 days by 5 units per day then 40/(n+1)=5 --> n=7.

_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 12890
Followers: 561

Kudos [?]: 158 [0], given: 0

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

18 Jul 2014, 10:52
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Intern
Joined: 09 Feb 2014
Posts: 8
Followers: 0

Kudos [?]: 5 [0], given: 25

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

21 Oct 2014, 12:25
Bunuel 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

(average production for n days) * n = (total production for n days) --> 50n=(total production for n days);
(total production for n days) + 90 = (average production for n+1 days) * (n+1) --> 50n + 90 = 55 * (n+1) --> n=7.

Or as 40 extra units increased the average for n+1 days by 5 units per day then 40/(n+1)=5 --> n=7.

Could you explain why there is n+1 days? I don't quite get the logic here. Thanks in advance.
Math Expert
Joined: 02 Sep 2009
Posts: 35912
Followers: 6851

Kudos [?]: 90029 [0], given: 10402

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

21 Oct 2014, 13:13
trambn wrote:
Bunuel 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

(average production for n days) * n = (total production for n days) --> 50n=(total production for n days);
(total production for n days) + 90 = (average production for n+1 days) * (n+1) --> 50n + 90 = 55 * (n+1) --> n=7.

Or as 40 extra units increased the average for n+1 days by 5 units per day then 40/(n+1)=5 --> n=7.

Could you explain why there is n+1 days? I don't quite get the logic here. Thanks in advance.

The past n days plus today, so one more day = n + 1 days.
_________________
Manager
Joined: 17 Mar 2014
Posts: 92
Followers: 0

Kudos [?]: 36 [0], given: 197

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

23 Oct 2014, 11:45
For past n days, average daily production is 50.
Today's average production of 90 unit raises average for (n+1)days by 55.

Weight Average formula.

(n*daily average+1*today's average) = 55
(n+1)

n*55 + 1*90 = 55
(n+1)

n=7

OA is E
Manager
Status: I am not a product of my circumstances. I am a product of my decisions
Joined: 20 Jan 2013
Posts: 132
Location: India
Concentration: Operations, General Management
GPA: 3.92
WE: Operations (Energy and Utilities)
Followers: 4

Kudos [?]: 90 [1] , given: 68

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

23 Oct 2014, 21:16
1
KUDOS
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

For "N" days avg production was 50 Units

Today production of 90 Units raises avg to 55 Units

So 90 Units of today raises each of N days avg unit by 5 Units + 55 Units of today.

Considering that if 55 Units were produced today then remaining 35 Units of today add up to raise value from 50 Units to 55 Units. Implies that if 5 units each are given to "N" days then the avg will be 55 Units

So, 35 / 5 = 7

Therefore "N" = 7

Ans E
Senior Manager
Status: Math is psycho-logical
Joined: 07 Apr 2014
Posts: 443
Location: Netherlands
GMAT Date: 02-11-2015
WE: Psychology and Counseling (Other)
Followers: 2

Kudos [?]: 104 [0], given: 169

For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

15 Jan 2015, 04:50
Sort of same as above, but let me explain:

Start by writing down the formula for the mean:
M=S/N

From stem:
M=50
N=n days
S= unknown, but using the formula for the mean we have 50=S/n, S=50n.

So, it becomes:
50 = (50n)/n, which btw makes sense if you look at it matheatically too.

Now, we know that the new M=55 and the new n=one more than before, so new n=n+1. The new S is 90 plus the S we had before, so 50n+90.

Side by side:

50 = (50n)/n VS 55= (50n+90)/n+1

Use 55= (50n+90)/n+1 to solve for n:

55 = (50n+90)/n+1
50n+90 = 55n + 55
90 - 55 = 5n
35 = 5n
n = 7 ANS E
Intern
Joined: 27 Jan 2015
Posts: 3
Followers: 0

Kudos [?]: 0 [0], given: 16

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

10 Aug 2015, 22:28
I thought about this like a weighted average problem. Since 90 (the last day; weight of 1) is +35 above 55 (the new average) and 50 (all the previous days; weight of n) is -5 below 55. In order to reach the new average, the sum of everything above and below 55 must equal to 0, so...

+35(1) + -5n = 0
n = 7

(E)
Intern
Joined: 10 Oct 2013
Posts: 30
Followers: 0

Kudos [?]: 1 [0], given: 3

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

11 Aug 2015, 02:30
55(n+1) - 50n = 90

5n = 35
n = 7
Manager
Joined: 28 Jun 2015
Posts: 139
Concentration: Finance, Economics
GPA: 3.5
Followers: 0

Kudos [?]: 53 [1] , given: 19

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

11 Aug 2015, 03:40
1
KUDOS
1
This post was
BOOKMARKED
$$\frac{50n + 90}{n+1} = 55$$

$$50n + 90 = 55n + 55$$

$$5n = 35$$

$$n = 7$$. Ans (E).
_________________

I used to think the brain was the most important organ. Then I thought, look what’s telling me that.

Current Student
Joined: 12 Aug 2015
Posts: 307
Concentration: General Management, Operations
GMAT 1: 640 Q40 V37
GMAT 2: 650 Q43 V36
GMAT 3: 600 Q47 V27
GPA: 3.3
WE: Management Consulting (Consulting)
Followers: 4

Kudos [?]: 257 [0], given: 1474

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

26 Feb 2016, 10:44
n/new one = 35/5 hence

n/new one = 7/1
_________________

KUDO me plenty

Senior Manager
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 392
Followers: 21

Kudos [?]: 138 [0], given: 2

Re: For the past n days, the average (arithmetic mean) daily [#permalink]

### Show Tags

13 Jul 2016, 06:45
1
This post was
BOOKMARKED
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

average = sum/quantity

We are given that the initial quantity is n days and that the average for those n days is 50 units. We can use this to determine a sum for the n days.

Since sum = average x quantity, we know:

sum = (50) (n) = 50n

We are next given that today, the production was 90 units. This means we can add “1” to the current quantity and “90” to the current sum. We are also given that this new average is 55 units per day. Substituting this information into the average formula we get:

55 = (50n + 90)/(n + 1)

55(n + 1) = 50n + 90

55n + 55 = 50n + 90

5n = 35

n = 7 days

_________________

Jeffrey Miller
Jeffrey Miller

Re: For the past n days, the average (arithmetic mean) daily   [#permalink] 13 Jul 2016, 06:45
Similar topics Replies Last post
Similar
Topics:
2 A bakery sold an average(arithmetic mean) of 820 cookies per day in an 2 18 Oct 2016, 19:37
5 If the average (arithmetic mean) of the four numbers 3, 15, 32, and (N 5 14 Oct 2015, 20:22
4 Given that a is the average (arithmetic mean) of the first n 6 22 Jul 2013, 10:12
5 For the past n days, the average (arithmetic mean) daily pro 5 19 Feb 2011, 05:21
6 The average (arithmetic mean) of the multiples of 6 5 28 May 2010, 12:57
Display posts from previous: Sort by