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Register now and save up to $200 Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code ## OG 13 - PS 145 tagged by: Brent@GMATPrepNow This topic has 5 expert replies and 1 member reply gdshamain Senior | Next Rank: 100 Posts Joined 09 Jan 2014 Posted: 41 messages #### OG 13 - PS 145 Sat May 03, 2014 1:34 pm 145. In a small snack shop, the average(arithmetic mean) revenue was$400 per day overall 10-day period.
During this period,if the average daily revenue was
$360 for the first 6 days,what was the average daily revenue for the last 4 days? (A)$420
(B) $440 (C)$450
(D) $460 (E)$480

Just wanted to know an alternate method for this one.
Can we solve this problem using weighted average logic ? ( with the horizontal axes logic)

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DavidG@VeritasPrep Legendary Member
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Mon Jun 29, 2015 7:54 am
Quote:
145. In a small snack shop, the average(arithmetic mean)
revenue was $400 per day overall 10-day period. During this period,if the average daily revenue was$360 for the first 6 days,what was the average daily
revenue for the last 4 days?
(A) $420 (B)$440
(C) $450 (D)$460
(E) $480 Just wanted to know an alternate method for this one. Can we solve this problem using weighted average logic ? ( with the horizontal axes logic) We could also do a little fancy number line action. If the average revenue was$360 for the first 6 days, and we're looking for the average revenue for last 4 days, we can depict the distance of each value from the overall average ($400) as 4x and 6x. See here: If 4x = 40, then x = 10 and 6x = 6*10 = 60. 400 + 60 = 460. _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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Matt@VeritasPrep GMAT Instructor
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Mon Jun 29, 2015 3:19 pm
Another approach:

To have an average of $400 over 10 days, we need total revenue of$400*10 = $4000. So far we have$360*6 = $2160, so we need$4000 - $2160 =$1840 over four days. $1840 / 4 =$460, and we're done!

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Rich.C@EMPOWERgmat.com Elite Legendary Member
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Sat May 03, 2014 2:02 pm
Hi gdshamain,

There are a number of ways to "do the math" on this type of question. Using the standard Average Formula will work perfectly here, and you'll be asked to use it a couple of times over the course of the Quant section, so you shouldn't try to avoid it.

That having been said, there's a weighted average "pattern" that can be used against this question:

The average of the 10 days = $400 The average for the first 6 days =$360. This means that, on each of the first 6 days, each day was $40 "behind" the average. To get the average "up" to$400, the remaining 4 days have to "make up" for that deficitâ€¦

6 x $40 =$240 "behind"

The last 4 days have to be above 400 by an amount that will make up for the $240.$240/4 = $60. This means that each of the last 4 days needs to be$460 for the overall average to be $400. Final Answer: D GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com gdshamain Senior | Next Rank: 100 Posts Joined 09 Jan 2014 Posted: 41 messages Sat May 03, 2014 2:29 pm Thanks for the explanation Rich. ### GMAT/MBA Expert Brent@GMATPrepNow GMAT Instructor Joined 08 Dec 2008 Posted: 11278 messages Followed by: 1225 members Upvotes: 5254 GMAT Score: 770 Sat May 03, 2014 4:51 pm gdshamain wrote: 145. In a small snack shop, the average(arithmetic mean) revenue was$400 per day overall 10-day period.
During this period, if the average daily revenue was
$360 for the first 6 days, what was the average daily revenue for the last 4 days? (A)$420
(B) $440 (C)$450
(D) $460 (E)$480

Here's another approach:

If the average (mean) daily revenue over 10 days is $400/day, then the TOTAL 10-DAY REVENUE = (10)($400) = $4000 The average daily revenue for the first 6 days is$360. So, the TOTAL 6-DAY REVENUE = (6)($360) =$2160

So, the TOTAL REVENUE for the last 4 days = $4000 -$2160 = $1840 So, the AVERAGE daily revenue for those 4 days =$1840/4 = $460 Answer: D Cheers, Brent _________________ Brent Hanneson â€“ Founder of GMATPrepNow.com Use our video course along with Check out the online reviews of our course Come see all of our free resources GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months! ### GMAT/MBA Expert Scott@TargetTestPrep GMAT Instructor Joined 25 Apr 2015 Posted: 781 messages Followed by: 3 members Upvotes: 43 Mon Jun 29, 2015 7:20 am gdshamain wrote: 145. In a small snack shop, the average(arithmetic mean) revenue was$400 per day overall 10-day period.
During this period,if the average daily revenue was
$360 for the first 6 days,what was the average daily revenue for the last 4 days? (A)$420
(B) $440 (C)$450
(D) $460 (E)$480

Just wanted to know an alternate method for this one.
Can we solve this problem using weighted average logic ? ( with the horizontal axes logic)
Solution:

This problem tests us on our knowledge of weighted averages. To solve, we set up a weighted average equation:

(Revenue for first 6 days + Revenue for final 4 days)/10 days = 400

We know that the average revenue for the first 6 days was \$360, resulting in total revenue for the first 6 days as 2,160. We let r be the average daily revenue for the final four days, so we have

(360 x 6 + 4r)/10 = 400

2,160 + 4r = 4,000

4r = 1,840

r = 460

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Scott Woodbury-Stewart Founder and CEO

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