List R contains five numbers that have an average value of 55. If the median of the numbers in the list is equal to the mean and the largest number is equal to 20 more than two times the smallest number, what is the smallest possible value in the list?

a. 35
b. 30
c. 25
d. 20
e. 15

Any suggestions about how to approach maximization/minimization problems?

Hi,
in these cases take the values opposite of what you are looking for..

lets take this Q..
we are given median= mean..
so 55 is middle number..
let the smallest be x, largest=2x+20..
now for making the x smallest possible, lets take the value of remaining numbers as large as possible..
so the 2nd largest = largest=2x+20,...
the secon smallest will be equal to the next bigger, which is the median..
th enumbers are x,55,55,2x+20,2x+20..
the total= 5* 55=275..
so x+55+55+2x+20+2x+20=275,...
5x+150=275..
x=25..
so the smallest value will be 25..
ans C..
hope it helped..
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Quality Question.
Here is my solution to this one =>

Let the 5 numbers in set R in increasing order be
R1
R2
R3
R4
R5


Now Using

\(Mean = \frac{Sum}{#}\)


Sum(5) = 55*5 = 275

The Question stem Also says that Mean= Median
#=5=Odd
Hence Median = 3rd element => R3

Hence R3=55
R5=20+2R1(Given)

Now,Here we are asked the minimum possible value of R1

R1 would be minimum when all other elements are maximum
R1=R1
R2=Median =55
R3=55
R4=R5=2R1+20

Hence adding them up we get =>

R1+55+55+2R1+20+2R1+20=275
Hence 5R1=125=> R1=25



Hence C


Great Question.
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Hi Bunuel,

I used the following approach.

Since mean is equal to median, the series is equally spaced.

So using the following formula :-

Sum= Average * number of items in the series= 55* 5= ((First number + Second Number)/2)*Number of items.
If x is the largest number and s the smallest number.
x=2s+ 20.

Therefore,
((2s+20+s)/2)*5=275.
Solving this I got smallest number=s=30.
What am I missing here. Please help.

Hi All,

While this question can be solved with Algebra, it can also be solved by TESTing THE ANSWERS.

We're given a lot of little pieces of information to work with, so we have to stay organized:
1) 5 numbers with an average of 55. This means that 5(55) = 275 is the SUM of these 5 numbers.
2) The question does NOT state that the numbers need to be distinct, so DUPLICATES ARE ALLOWED.
3) The median = mean = 55. The 3rd value of the 5 numbers MUST be 55.
4) The largest number = 2(smallest number) + 20.

The question asks us for the smallest POSSIBLE value in the list. Let's start by TESTing the smallest answer….

Answer E: 15

If the smallest number was 15, then the largest would be 50. This is NOT possible (the average and median are both 55).

Answer D: 20

If the smallest number was 20, then the largest would be 60. This is NOT possible (the sum of the other 3 values = 195; there's no way to get to a total of 195 with the 3 remaining values and the above restrictions).

Answer C: 25

If the smallest number was 25, then the largest would be 70. This IS POSSIBLE. The sum of the other 3 values would be 180 (with a 70, a 55 and another 55, we would get a total of 180).

Final Answer:

GMAT assassins aren't born, they're made,
Rich
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