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by SubratGmat2011 » Thu Sep 23, 2010 7:14 pm
In the number 1.4ab5, a and b represent single positive digits. If x = 1.4ab5, what is the value of 10 - x?

(1) If x is rounded to the nearest hundredth, then 10 - x = 8.56.

(2) If x is rounded to the nearest thousandth, then 10 - x = 8.564.
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by limestone » Thu Sep 23, 2010 8:07 pm
1. x rounded to the nearest hundredth : x(rounded) =10 - 8.56 = 1.44
We can not know whether 1.4ab5 is rounded up or rounded down to 1.44
x can be either 1.4365 (round up) or 1.4415 (round down). => insuff

2. x is rounded to the nearest thousandth: x(rounded) = 10 - 8.564 = 1.436
1.4ab5 if rouded wil become 1.4a(b+1) (b+1 is consider 1 digit) and if b+1 = 10, then the thousandth digit will be 0, the hundredth digit a will be added 1.
However x(rounded) = 1.436 then b+1 = 6 then a = 3 ( if b+1 = 0, then a +1 =3))
Hence b = 6-1 =5, a =3, x= 1.4355 =>suff

Pick B, only 2 is suff.
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by Brent@GMATPrepNow » Thu Oct 10, 2019 5:25 am
SubratGmat2011 wrote:In the number 1.4ab5, a and b represent single positive digits. If x = 1.4ab5, what is the value of 10 - x?

(1) If x is rounded to the nearest hundredth, then 10 - x = 8.56.

(2) If x is rounded to the nearest thousandth, then 10 - x = 8.564.
Target question: What is the value of 10 - x?

Given: X = 1.4ab5

Statement 1: If x is rounded to the nearest hundredth, then 10 - x = 8.56
10 - 1.44 = 8.56
So, x rounded to the nearest HUNDREDTH = 1.44
So, x COULD equal 1.4355, 1.4365, 1.4375, 1.4385, 1.4395, 1.4405, 1.4415, 1.4425, 1.4435 OR 1.4445
Given all of the different possible values of x, 10 - x could have MANY different values.
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: If x is rounded to the nearest thousandth, then 10 - x = 8.564
10 - 1.436 = 8.564
In other words, x rounded to the nearest THOUSANDTH = 1.436
This tells us that a must equal 3, leaving us with 1.43b5
If 1.43b5 rounded to the nearest THOUSANDTH = 1.436, then b MUST equal 5
So, x must equal 1.4355, which means 10 - x MUST equal 8.5645
Since we can answer the target question with certainty, statement 2 is SUFFICIENT

Answer: B

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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