MathRevolution wrote:
[GMAT math practice question]
Four values from a data set of 5 elements are 10, 10, 11, and 11. What is the fifth data value?
1) The range of the data set is 2
2) The average of the data values is greater than 10
Let's say that x = the missing data valueTarget question: What is the value of x? Given: The other 4 values are 10, 10, 11 and 11 Statement 1: The range of the data set is 2 So, (the biggest value) - (the smallest value) = 2
The problem here is that x COULD be the smallest value, or x COULD be the biggest value
Consider these two possible cases:
Case a: x = 9. In this case, the numbers are {9, 10, 10, 11, 11}, so the range is 2. Here, the answer to the target question is
x = 9Case b: x = 12. In this case, the numbers are {10, 10, 11, 11, 12}, so the range is 2. Here, the answer to the target question is
x = 12Since we cannot answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: The average of the data values is greater than 10There are infinitely many values of x that satisfy statement 2. Here are two:
Case a: x = 1000. In this case, the average is definitely greater than 10. Here, the answer to the target question is
x = 1000Case b: x = 2000. In this case, the average is definitely greater than 10. Here, the answer to the target question is
x = 2000Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Statements 1 and 2 combined Statement 1 tells us that EITHER x = 9 OR x = 12
Statement 2 tells us that the average of the data values is greater than 10
Let's examine the averages for each case (i.e., x = 9 and x = 12)
If
x = 9, then the average of the 5 values = (9 + 10 + 10 + 11 + 11)/5 = 51/5 = 10.2
If
x = 12, then the average of the 5 values = (10 + 10 + 11 + 11 + 12)/5 = 54/5 = 10.8
In BOTH cases, the average is greater than 10
So, the answer to the target question is
EITHER x = 9 OR x = 12Since we cannot answer the
target question with certainty, the combined statements are NOT SUFFICIENT
Answer: E
Cheers,
Brent