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1) The distance between Z and 10 is lesser than distance between Z and X. So Z is greater than the center of the line segment X to 10. That means Z is greater than the average of X and 10. Sufficient. 2) Z = 5X If X=1, then Z = 5. Avg of X and 10 = 5.5. So Z<Avg. If X=2, then Z = 10. Avg of X and 10 = 6. So Z>Avg. Statement is Insufficient.

Can anyone please suggest me the solution. I arrived at B, but unfortunately it was wrong. Thanks.

If x is a positive number less than 10, is z greater than the average (arithmetic mean) of x and 10?

Given: 0<x<10. Q: is z greater than the average of x and 10? Or: is z>\frac{10+x}{2}? --> 2z>10+x?

(1) On the number line, z is closer to 10 than it is to x --> |10-z|<|z-x| --> as z is closer to 10 than it is to x, then z>x, so |z-x|=z-x --> two cases for 10-z:

A. z\leq{10} --> |10-z|=10-z --> |10-z|<|z-x| becomes: 10-z<z-x --> 2z>10+x. Answer to the question YES.

B. z>{10} --> in this case 2z>20 and as x<10, then x+10<20, hence 2z>10+x. Answer to the question YES.

OR another approach: Given: x-----average-----10----- (average of x and 10 halfway between x and 10).

Now, as z is closer to 10 than it (z) is to x, then z is either in the blue area, so more than average OR in the green area, so also more than average. Answer to the question YES.

Sufficient.

(2) z = 5x --> is 2z>10+x? --> is 10x>10+x? --> is x>\frac{10}{9}. We don't now that. Not sufficient. (we've gotten that if x>\frac{10}{9}, then the answer to the question is YES, but if 0<x\leq{\frac{10}{9}}, then the answer to the question is NO.)

Re: x is a positive number less than 10 [#permalink]
19 Apr 2011, 15:29

1

This post received KUDOS

Expert's post

If x is a positive number less than 10 is z greater than the average of x and 10?

1) on the number line, z is closer to 10 than it is to x

2) z=5x

Drawing a number line can help you see the answer quickly.

Attachment:

Ques2.jpg [ 4.71 KiB | Viewed 6032 times ]

So x is somewhere between 0 and 10 and average of x and 10 is between x and 10. z can be in any of the 5 regions as shown.

1) on the number line, z is closer to 10 than it is to x

In which regions is z closer to 10 than to x? Only the two rightmost regions. There, z is greater than the average of x and 10. Sufficient.

2) z = 5x Put x = 1 z = 5 but average of 1 and 10 is 5.5 so z is less than the average. Actually, this is where I stop and mark (A) as the answer without checking to see if there is a value of x for which z is greater than the average. Think, why?
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Re: x is a positive number less than 10 [#permalink]
19 Apr 2011, 20:50

1

This post received KUDOS

@Karishma We stop in (2) because we've found something contrary to the answer in (1), while in earlier choice we had a definite answer. So the answer can't be B,C,D oe E.

The goal in DS is to get No as answer first for the choices, or to find the inconsistencies.

Re: x is a positive number less than 10 [#permalink]
20 Apr 2011, 03:28

Expert's post

subhashghosh wrote:

@Karishma We stop in (2) because we've found something contrary to the answer in (1), while in earlier choice we had a definite answer. So the answer can't be B,C,D oe E.

The goal in DS is to get No as answer first for the choices, or to find the inconsistencies.

From the diagram above, it's evident that the answer is Yes

(2) is insufficient

if x is very close to 0, then z may not be closer to 10

e.g, x = 0.1, then z = 0.5

if x = 2, then z = 10 (greater than average)

Answer - A

Yes, it is not possible to get inconsistent answers from the two statements i.e. we cannot have 'Yes. z is greater. Sufficient Alone.' from statement 1 and 'No. z is smaller. Sufficient Alone.' from statement 2. From statement 2, we will either get 'Yes. z is greater. Sufficient Alone.' or 'z can be smaller or greater so not sufficient alone'

From statement 1, we got that z is greater than the average. From statement 2, we tried a value and we got that z is less than the average. Then there must be a value for which z is greater than the average too in statement 2. We don't even need to try it. Definitely statement 2 alone is not sufficient and answer is (A).
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If x is a positive number less than 10, is z greater than th [#permalink]
24 Apr 2012, 08:18

If x is a positive number less than 10, is z greater than the average(Arithmetic mean) of x and 10? 1. On the number line, z is closer to 10 than it is to x. 2. z = 5x.

Re: If x is a positive number less than 10, is z greater than th [#permalink]
24 Apr 2012, 09:28

Expert's post

gayathriz wrote:

If x is a positive number less than 10, is z greater than the average(Arithmetic mean) of x and 10? 1. On the number line, z is closer to 10 than it is to x. 2. z = 5x.

Please explain your answer choice. Thanks

Merging similar topics. Please ask if anything remains unclear.
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Re: If x is a positive number less than 10, is z greater than [#permalink]
13 Oct 2013, 06:57

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