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Bunuel
If the prices of four of the five books that Ann bought are $4, $6, $10, and $12, what is the price of the fifth book that Ann bought?

(1) The price of the fifth book that Ann bought is greater than $8.

This information alone is clearly insufficient.

(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.

Assuming the price of the fifth book is $x, the average price would be (4 + 6 + 10 + 12 + x)/5.

Our set of values is {4, 6, 10, 12, x}. Note that the given set can have only three possible medians:


  • 6, when \(x \leq 6\)
  • x, when \(6 \leq x \leq 10\)
  • 10, when \(10 \leq x\)

When the median is 6, equating the average and the median gives us (4 + 6 + 10 + 12 + x)/5 = 6, resulting in x = -2. Discard this value because a price cannot be negative.

When the median is x, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = x, resulting in x = 8.

When the median is 10, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = 10, resulting in x = 18.

Hence, we have two possible prices for the fifth book: $8 and $18.

Not sufficient.

(1)+(2) Since from (1) x > 8, we are left with only x = 18 from (2). Sufficient.

Answer: C.
­but isnt this a rule that when median=mean then the values are in AP? if yes, the statement B alone was giving me median=mean=8
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If the prices of four of the five books that Ann bought are $4, $6, $10, and $12, what is the price of the fifth book that Ann bought?

(1) The price of the fifth book that Ann bought is greater than $8.
(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.

$4, $6, $10, and $12

Note that the average of these given 4 values is $8.

(1) The price of the fifth book that Ann bought is greater than $8.

It could be anything $8.5, $9, $28 etc. Not sufficient.


(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.

The 5th book's price could be $8. Then it would be mean and median. Or it could be much higher with mean = median = 10.
If mean were 10, the fifth book's price would be $18.
Not sufficient.


Using both, the fifth book's price cannot be $8. If the price is greater than 8, it cannot be between 8 and 10 because then it would be the median but not the mean. Say if we were to assume that cost of the 5th book is $9, it would be median but cannot be mean. Mean of other number is 8. So overall mean will become more than 8.

Hence the median and mean must be 10 and the price of the fifth book must be $18. Note that no other value can be the median since 10 can be the greatest third number in the list.
So price of the fifth book that Ann bough is $18. Sufficient

Answer (C)

Here is another question on mean median in DS: https://youtu.be/T_sPj1EKmn0
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Bunuel
If the prices of four of the five books that Ann bought are $4, $6, $10, and $12, what is the price of the fifth book that Ann bought?

(1) The price of the fifth book that Ann bought is greater than $8.

This information alone is clearly insufficient.

(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.

Assuming the price of the fifth book is $x, the average price would be (4 + 6 + 10 + 12 + x)/5.

Our set of values is {4, 6, 10, 12, x}. Note that the given set can have only three possible medians:


  • 6, when \(x \leq 6\)
  • x, when \(6 \leq x \leq 10\)
  • 10, when \(10 \leq x\)

When the median is 6, equating the average and the median gives us (4 + 6 + 10 + 12 + x)/5 = 6, resulting in x = -2. Discard this value because a price cannot be negative.

When the median is x, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = x, resulting in x = 8.

When the median is 10, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = 10, resulting in x = 18.

Hence, we have two possible prices for the fifth book: $8 and $18.

Not sufficient.

(1)+(2) Since from (1) x > 8, we are left with only x = 18 from (2). Sufficient.

Answer: C.
­but isnt this a rule that when median=mean then the values are in AP? if yes, the statement B alone was giving me median=mean=8

I also think the answer should be B. By testing 2-3 cases to the equation 32+x=5m, if letting m be median, we can quickly find x= 8 is the only solution that median is 8 as well.
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Bunuel
If the prices of four of the five books that Ann bought are $4, $6, $10, and $12, what is the price of the fifth book that Ann bought?

(1) The price of the fifth book that Ann bought is greater than $8.

This information alone is clearly insufficient.

(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.

Assuming the price of the fifth book is $x, the average price would be (4 + 6 + 10 + 12 + x)/5.

Our set of values is {4, 6, 10, 12, x}. Note that the given set can have only three possible medians:


  • 6, when \(x \leq 6\)
  • x, when \(6 \leq x \leq 10\)
  • 10, when \(10 \leq x\)

When the median is 6, equating the average and the median gives us (4 + 6 + 10 + 12 + x)/5 = 6, resulting in x = -2. Discard this value because a price cannot be negative.

When the median is x, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = x, resulting in x = 8.

When the median is 10, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = 10, resulting in x = 18.

Hence, we have two possible prices for the fifth book: $8 and $18.

Not sufficient.

(1)+(2) Since from (1) x > 8, we are left with only x = 18 from (2). Sufficient.

Answer: C.
­but isnt this a rule that when median=mean then the values are in AP? if yes, the statement B alone was giving me median=mean=8

I also think the answer should be B. By testing 2-3 cases to the equation 32+x=5m, if letting m be median, we can quickly find x= 8 is the only solution that median is 8 as well.



Statement 2 alone - Look at this:

$4, $6, $8, $10, $12
Mean = median = 8
Fifth book price = 8


$4, $6, $10, $12, $18
Mean = median = 10
Fifth book price = 18
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If the prices of four of the five books that Ann bought are $4, $6, $10, and $12, what is the price of the fifth book that Ann bought?

(1) The price of the fifth book that Ann bought is greater than $8.
(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.
Question: Price of 5th book = x = ?

Statement 1: x > 8

NOT SUFFICIENT

Statement 2:Mean = median

The set so far = {4, 6, 10, 12, x} where placement of x is uncertain

Mean = Sum {4, 6, 10, 12, x} / 5 = (32+x)/5 = 6.4+(x/5)

Since Mean is definitely greater than 6.4 so the median should also be greater than 6.4

Case 1: If Median = 10, then mean = 10 then sum = 50 then x = 18

Case 2: If Median = x, then 6.4+(x/5) = x then x = 8

NOT SUFFICIENT


Combining the statements

X > 8 and Mean = Median

i.e. only possible solution left is Case 1 of Statement 2 i.e.x = 18

SUFFICIENT

Answer: Option C
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KarishmaB GMATinsight I read somewhere that both the statements should not clash with each other, so when using statements we arrive at x=8, it is clashing with statement 1, how to go about this confusion?
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KarishmaB GMATinsight I read somewhere that both the statements should not clash with each other, so when using statements we arrive at x=8, it is clashing with statement 1, how to go about this confusion?

It is correct that the ANSWER you get from the two statement cannot clash, but both statements can have extraneous values.

So this is NOT possible:
Statement 1 is sufficient and tells us that x = 18
Statement 2 is sufficient and tells us that x = 10

But this is possible:
Statement 1 is not sufficient and tells us that x = 10 or 18
Statement 2 is not sufficient and tells us that x = 10 or 100
So both together tell us that x = 10

Basically, at least one value MUST overlap.

In our original question,
Statement 1 is not sufficient and tells us that x > 8 so it can be 8.5 or 9 or 18 or 1000 etc
Statement 2 is not sufficient and tells us that x = 8 or 18
Together they tell us that x = 18.
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Beautiful explanation. I like how the combination of 1 + 2 took just seconds because of the analysis of B. thanks Bunuel.
Bunuel
If the prices of four of the five books that Ann bought are $4, $6, $10, and $12, what is the price of the fifth book that Ann bought?

(1) The price of the fifth book that Ann bought is greater than $8.

This information alone is clearly insufficient.

(2) The median price of the five books that Ann bought is equal to the average (arithmetic mean) price of 5 books.

Assuming the price of the fifth book is $x, the average price would be (4 + 6 + 10 + 12 + x)/5.

Our set of values is {4, 6, 10, 12, x}. Note that the given set can have only three possible medians:

  • 6, when \(x \leq 6\)
  • x, when \(6 \leq x \leq 10\)
  • 10, when \(10 \leq x\)


When the median is 6, equating the average and the median gives us (4 + 6 + 10 + 12 + x)/5 = 6, resulting in x = -2. Discard this value because a price cannot be negative.

When the median is x, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = x, resulting in x = 8.

When the median is 10, equating the average and the median gives (4 + 6 + 10 + 12 + x)/5 = 10, resulting in x = 18.

Hence, we have two possible prices for the fifth book: $8 and $18.

Not sufficient.

(1)+(2) Since from (1) x > 8, we are left with only x = 18 from (2). Sufficient.

Answer: C.
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