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Grockit blog DS

by GmatKiss » Sat Oct 15, 2011 4:08 pm
For a certain company X, the average daily payroll for each 30-day payroll cycle is the average (arithmetic mean) of the daily payroll totals for each of the 30 days. During the first part of a recent 30-day payroll cycle, the daily payroll was a constant $5,750. When a new employee was hired during this 30-day cycle, the total payroll for each day rose by $280. If the new daily payroll total remained constant for the remainder of the cycle, what was the average daily payroll for the 30-day cycle?

(1) The new employee was hired on the 11th day of the payroll cycle.

(2) The average daily payroll was $5,890 through the first 20 days of the cycle.

IMO: B
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Source: — Data Sufficiency |
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by pemdas » Sat Oct 15, 2011 8:16 pm
looks like @grockit beefs ups its DS questions with much verbiage as like these are Reading comprehension lines

from the very beginning you can cross out the first sentence and read only 30 days and daily average :)

we have in our question the following conditions:

Total daily payrolls/number of days (only possible days, not employees! please consider note below)= Average daily payroll

note: in the first part of 30-day period the average daily payroll was 5750 and within the 20-day period the average daily payroll was set as 5890. This should mean that our total daily payroll amounts differ.

put Total daily payrolls=a, number of days=b and Average daily payroll is 5750, then a/b=5750


st(1) says that (30-b)=20 (the new employee was hired on the 11th day) and we solve for a and b, and find the average 30-day payroll

30-b=20, b=10; a=57500 the first part's total payrolls
and 20*5750+20*280 will give us the remaining days' total payroll
their average should give us the average 30-day payroll => (20*5750+20*280 + 57500)/3=5843.33 Sufficient
st(2) 5890*20=117800 (the average daily payroll was 5890 throughout the first 20 days). The remaining 10 days total payrolls' amount was 10*5750=57500. The 30-day total payrolls' amount was (57500+117800)/30=5843.33 Sufficient;

iom d
GmatKiss wrote:For a certain company X, the average daily payroll for each 30-day payroll cycle is the average (arithmetic mean) of the daily payroll totals for each of the 30 days. During the first part of a recent 30-day payroll cycle, the daily payroll was a constant $5,750. When a new employee was hired during this 30-day cycle, the total payroll for each day rose by $280. If the new daily payroll total remained constant for the remainder of the cycle, what was the average daily payroll for the 30-day cycle?

(1) The new employee was hired on the 11th day of the payroll cycle.

(2) The average daily payroll was $5,890 through the first 20 days of the cycle.

IMO: B
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