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In a small snack shop, the average (arithmetic mean) revenue was $400 per day over a 10-day period. During this period,

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In a small snack shop, the average (arithmetic mean) revenue was $400 per day over a 10-day period. During this period,

by Gmat_mission » Sat Aug 22, 2020 3:50 am

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In a small snack shop, the average (arithmetic mean) revenue was $400 per day over a 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

Answer: D

Source: GMAT Prep
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Re: In a small snack shop, the average (arithmetic mean) revenue was $400 per day over a 10-day period. During this peri

by Targt780 » Sat Aug 22, 2020 4:00 am
Given that

Average revenue over a 10 period is 400
Average revenue over the first 6 days is 360

Let the revenue per day be given by D1, D2, .... D10

Converting the above statements into equations we have

Statement (2)

\(\frac{D_1+D_2+D_3+D_4+D_5+D_6}{6}=360\)

Solving it we have

\(D_1+D_2+D_3+D_4+D_5+D_6\) = 360*6

\(D_1+D_2+D_3+D_4+D_5+D_6\) = 2160

Similarly statement (1) can be written as

\(D_1+D_2+D_3+D_4+D_5+D_6+D_7+D_8+D_9+D_10\) = 4000

Substituting the \(D_1+D_2+D_3+D_4+D_5+D_6\) value in the above equation we get

2160+\(D_7+D_8+D_9+D_10\) =4000

\(D_7+D_8+D_9+D_10\) =4000-2160

\(D_7+D_8+D_9+D_10\) = 1840

Now to find the average revenue over the last 4 days we need to divide \(D_7+D_8+D_9+D_10\) by 4

Average revenue over the last 4 days = \(\frac{D_7+D_8+D_9+D_{10}}{4}=\frac{1840}{4}=460\)

hence the OA is D
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Re: In a small snack shop, the average (arithmetic mean) revenue was $400 per day over a 10-day period. During this peri

by Brent@GMATPrepNow » Sat Aug 22, 2020 5:45 am
Gmat_mission wrote: ↑
Sat Aug 22, 2020 3:50 am
 In a small snack shop, the average (arithmetic mean) revenue was $400 per day over a 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

Answer: D

Source: GMAT Prep
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
Brent Hanneson - Creator of GMATPrepNow.com
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