akhileshgupta05 wrote:
The Range of Set A is R. A number having equal value to R, is added to set A. Will the range of Set A increase ?
(1) All numbers in Set A are positive.
(2) The mean of the new set is smaller than R.
Source: 800Score Tests.
Because we are given a set of numbers, we can assume that all numbers are distinct, and that we have at least two numbers.
Let's denote by \(M\) the largest value of the set, and by \(m\) its smallest value. Then the range is \(R = M - m\).
The given question can be reformulated as "Is \(R < m\) or \(R>M\)?" If \(m\leq{R}\leq{M},\) the range of the set A will remain the same after adding \(R.\)
(1) If \(R=M-m<m,\) then \(\,\,M<2m.\)
If \(R=M-m>{m},\) then \(\,\,M>{2m}.\)
All the numbers in the set A being positive, both inequalities are possible. In addition, \(R=M-m<M.\)
So, \(R\) can be smaller or greater than the smallest element in the set, but for sure, it is smaller than the largest element.
Not sufficient.
(2) Let's denote by \(A_n\) the average of the set A before we add \(R\) to it.
Then \(\frac{A_n\cdot{n}+R}{n+1}<R,\) from which \(A_n\cdot{n}+R<nR+R\), or \(A_n<R.\)
Since the average \(A_n\geq{m}\) we can deduce that \(R>m.\)
But if \(m\) is negative, \(R=M-m>M\). If \(m\) is positive, then necessarily \(R=M-m<M.\)
Not sufficient.
(1) and (2) together: from the above analysis, we can see that if \(m>0,\) then \(R\) is between \(m\) and \(M,\) and the range will remain the same.
Sufficient.
Answer C.
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