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The formatting of this question is unclear. Is the question referring to 6 different variables (using subscript) or is it referring to 1 variable with 6 different exponents?

Re: What is the average (arithmetic mean) of x1,x2,x3,x4,x5,x6 ? [#permalink]

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17 May 2015, 19:57

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reto wrote:

What is the average (arithmetic mean) of x1,x2,x3,x4,x5,x6 ?

(1) The average of x1,x2,x3,x4 is 28. (2) The average of x4,x5,x6 is 21.

Given 6 Numbers : \(x_1,x_2,x_3,x_4,x_5,x_6\) , what is average of these 6 numbers ?

(1) The average of \(x_1,x_2,x_3,x_4\) is 28. no info about \(x_5,x_6\) . NS (2) The average of \(x_4,x_5,x_6\) is 21. no info about \(x_1,x_2,x_3\) . NS

Together : Brute force approach(we know that \(x_4\) is not known so answer is E but lets see why still insufficient) \(x_1+x_2+x_3+x_4 = 28*4=112\) and \(x_4+x_5+x_6=21*3=63\)

So, \(x_1+x_2+x_3+x_4 +x_5 +x_6 = 175-x_4\) Average= \(\frac{x_1+x_2+x_3+x_4 +x_5 +x_6}{6} = \frac{175-x_4}{6}\) we do not know \(x_4\) (it can be 0, or any other value) so the answer is E .
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Would like to know why E is the answer, and what is wrong with my logic

Hi

So your first equation is: x1+x2+x3+x4 = 112 and your second equn is: x4+x5+x6 = 63

If you add the above two equations, you will get: x1+x2+x3+x4+x5+x6+x4 = 175 Or Total Sum+x4 = 175. Since we dont know x4, we cant find the total sum

Or instead of adding if we subtract the above two equations, x1+x2+x3-x5-x6 = 49. How does it give us the total sum? or how does it give us the value of x4? It doesnt. It only tells us that x4 will be subtracted and thus eliminated, and we are left with x1+x2+x3-x5-x6.. this doesnt help us to get the required sum at all.