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But after multiplying every number by N,N will come into picture for new mean. And if you don't know N u can't calculate the % increase. Taking statement A into effect Old Mean = 120/6 New mean = 120N/6

If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase? (A) Z = 60 (B) N = Z / M

I don't have answer for this.But I think answer should be

. X {-14, -12, 17, 28, 41, Z} If all the numbers are multiplied by a constant, the mean will also increase by that constant.

1. Z=60

We get a mean of 20 here initially. If the set is multiplied by 10, the new mean becomes 200, increasing the mean by 900% If the set is multiplied by 2, the new mean becomes 40, increasing the mean by 100%

We must find an exact value of multiplier or mean to find the percent increase in mean. Not Sufficient.

2. N = Z / M

(-14, -12, 17, 28, 41 + Z)/6 = M

60+Z=6M N = Z / M; Z=NM

60+NM=6M. Not Sufficient to find an exact mean or multiplier. Not Sufficient.

Combining both; 60+NM=6M NM=Z=60 60+60=6M M = 120/6= 20 And N = Z/M = 60/20=3

We know the multiplier. Sufficient.

Ans: "C"

P.S.: The new mean will increase by 20% because the multiplier is 3. We wouldn't need "Z" if we knew the multiplier, however in this case; we needed Z to find the multiplier.
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Guys, Btw do you know where is Bunuel is these days? He is seldom online now.

You know what, "I was wondering about the same". Please come back soon Legend, we are deprived of your elegant solutions/approach. Perhaps "bb" can tell us where he is these days and when will he be coming back.
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Re: If every member of set X {-14, -12, 17, 28, 41, Z} is [#permalink]

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26 Jun 2013, 06:34

ANSWER : A

If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase? (A) Z = 60 (B) N = Z / M

ANS (A) : The set totals to 120 provided 60 (Z) is added to it and therefore the mean is 20. Now let's take an assumption for "N" i.e 2 and multiply it. So the the mean now is 40 which is 200 % of 20. Therefore sufficient. Further N can be assumed as odd no. and the % can be calculated therefore sufficient.

ANS (B) : N, here can be assumed as a number but what is Z (can be any no. again) and the mean depends on Z. Therefore insufficient. AD/BCE split

If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase? (A) Z = 60 (B) N = Z / M

ANS (A) : The set totals to 120 provided 60 (Z) is added to it and therefore the mean is 20. Now let's take an assumption for "N" i.e 2 and multiply it. So the the mean now is 40 which is 200 % of 20. Therefore sufficient. Further N can be assumed as odd no. and the % can be calculated therefore sufficient.

ANS (B) : N, here can be assumed as a number but what is Z (can be any no. again) and the mean depends on Z. Therefore insufficient. AD/BCE split

Please note that the OA for this question is C, not A.

When a DS question asks about the value of some variable, then the statement is sufficient ONLY if you can get the single numerical value of this variable.

Different N's will give you different numerical increase for (1).

If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase? (A) Z = 60 (B) N = Z / M

I don't have answer for this.But I think answer should be

. X {-14, -12, 17, 28, 41, Z} If all the numbers are multiplied by a constant, the mean will also increase by that constant.

1. Z=60

We get a mean of 20 here initially. If the set is multiplied by 10, the new mean becomes 200, increasing the mean by 900% If the set is multiplied by 2, the new mean becomes 40, increasing the mean by 100%

We must find an exact value of multiplier or mean to find the percent increase in mean. Not Sufficient.

2. N = Z / M

(-14, -12, 17, 28, 41 + Z)/6 = M

60+Z=6M N = Z / M; Z=NM

60+NM=6M. Not Sufficient to find an exact mean or multiplier. Not Sufficient.

Combining both; 60+NM=6M NM=Z=60 60+60=6M M = 120/6= 20 And N = Z/M = 60/20=3

We know the multiplier. Sufficient.

Ans: "C"

P.S.: The new mean will increase by 20% because the multiplier is 3. We wouldn't need "Z" if we knew the multiplier, however in this case; we needed Z to find the multiplier.

I don't understand how you know the mean will increase by 20% by knowing that the multiplier is 3 (and not needing to know "Z")

Re: If every member of set X {-14, -12, 17, 28, 41, Z} is [#permalink]

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07 Dec 2013, 05:51

If every member of set X {-14, -12, 17, 28, 41, Z} is multiplied by number N, by what percent will the mean M of the set increase?

(1) Z = 60 (2) N = Z / M

Solution: If we increase/decrease each term in a set by the same percent( multiply all the terms by a constant), mean will increase/decrease by same percent. So, to know the percent increase in the mean we have to find 'N'

(1) By knowing the value of Z, we can find the value M, but we do not know the value of 'N' : Insufficient (2) Since Z is unknown, we cannot find 'N': Insufficient

(1)+(2) By first we can find the values of Z and M, which are 60 and 20 respectively, and by (2) we can find 'N', which is 3 Sufficient

Re: If every member of set X {-14, -12, 17, 28, 41, Z} is [#permalink]

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18 Sep 2016, 04:21

2

This post received KUDOS

A) Z=60 by knowing the value of z we can calculate mean of set but for percent increase in mean when multiplied by N, value of N is required. Not suff B) N= Z/M without value of Z, M can't be found out and without value of M and Z, N can't be found out Not Suff So, combining we have value of Z and further value of M and N, hence percentage increase can be calculated Answer is C.

Re: If every member of set X {-14, -12, 17, 28, 41, Z} is [#permalink]

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01 Nov 2017, 01:40

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