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Re: Set V consists of 2 distinct positive values. What is the [#permalink]

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06 May 2012, 02:30

The answer seems to be (B) here.

Statement (1) is insufficient: Just knowing the mean is not enough. Statement (2): Let the numbers be x and x+10 Then their mean = x+5 S.D. = sqrt (50/2) = 5 Sufficient.

Re: Set V consists of 2 distinct positive values. What is the [#permalink]

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06 May 2012, 09:23

The answer has to be B. After simplifying the question, we can arrive to below: Let's assume the 2 distinct +ve numbers as x and y. Assuming y>x. Mean= x+y/2 S.D = SQRT(((x+y/2) -x)^2 + (y-(x+y/2))^2)/2) =SQRT(((x+y-2x)/2)^2 + ((2y-y-x)/2)^2/2) =SQRT((y-x)^2/2) =y-x/sqrt(2)...so we just need to know the diff between y and x and we get it from the 2nd statement which gives us the range.

Re: Set V consists of 2 distinct positive values. What is the [#permalink]

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02 Jun 2014, 01:43

We have two numbers. The question is about their standard deviation.

As the mean is ten, we have the following relationship for the two numbers(x1, x2): x1= 10-x, x2= 10+x. This does not help us to calculate the standard deviation. x could be 0, or extremely large.

Statement one is hence insufficient.

We're given the range, meaning that we now have the following relationship for x1 and x2: x1=x, x2=x(+ or -)10.

This helps us. We now know that one of the numbers is 5 above the mean and the other is 5 below the mean. We do not need the actual mean to calculate the deviation.

We get 5^2 and (-5)^2. Finding the variance = (25+25)/2 = 25 And the square root of 25=5 which is our standard deviation. However this was not asked of us.

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