greenwich wrote:If Mark saved an average (arithmetic mean) of $80 per week for 3 consecutive weeks, how much did he save the second week?
(1) The average amount that Mark saved per week for the first 2 weeks was $60.
(2) The amount that Mark saved the first week was 1/2 the amount he saved the second week and 1/3 the amount he saved the third week.
Sum = (number of weeks)(average per week).
Sum for the entire 3 weeks = 3*80 = 240.
Statement 1: The average amount that Mark saved per week for the first 2 weeks was $60.
Sum for the first 2 weeks = 2*60 = 120.
Thus, the amount saved in the 3rd week = (sum for the entire 3 weeks) - (sum for the first 2 weeks) = 240-120 = 120.
No way to determine the amount saved in the 2nd week.
INSUFFICIENT.
Statement 2: The amount that Mark saved the first week was 1/2 the amount he saved the second week and 1/3 the amount he saved the third week.
Thus, for every $1 saved in the 1st week, $2 is saved in the 2nd week, and $3 is saved in the 3rd week.
In other words:
1st week : 2nd week : 3rd week = 1:2:3.
Since we know the RATIO of the 3 weeks (1:2:3) and the SUM of the 3 weeks (240), we can determine the amount saved in each week.
SUFFICIENT.
The correct answer is
B.
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