Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 43867

Question Stats:
60% (01:16) correct 40% (01:57) wrong based on 65 sessions
HideShow timer Statistics



Math Expert
Joined: 02 Sep 2009
Posts: 43867

Re S9503 [#permalink]
Show Tags
16 Sep 2014, 00:49
Official Solution: We need to determine the number of incidents reported in 2005. The problem tells us that 1,000 incidents were reported in 2003. In 2004, \(x\) percent fewer incidents were reported, so \((100  x) \times 1,000\) incidents were reported. Since a percentage is equivalent to a fraction with a denominator of 100, we can express the number of incidents reported in 2004 as \(\frac{100  x}{100} \times 1,000\). In 2005, \(y\) percent more incidents were reported than in 2004. This can be expressed as \(\frac{100 + y}{100}(\frac{100  x}{100} \times 1,000)\). It is this target expression that we must find a value for. Multiply the numerators and denominators: \(\frac{100 + y}{100}(\frac{100  x}{100} \times 1,000) = \frac{1,000(100 + y )(100  x)}{10,000}\). Cancel 1,000 from the numerator and denominator and FOIL what remains: \(\frac{(100 + y)(100  x)}{10} = \frac{10,000  100x + 100y  xy}{10}\). Evaluating this expression will require either solving for \(x\) and \(y\) or finding a way to substitute a number for all variable terms. Statement 1 says that \(xy = 50\). This does not allow us to solve for either \(x\) or \(y\). We can substitute it into our target expression to get \(\frac{10,000  100x + 100y  50}{10}\), but doing so does not eliminate the need to solve for \(x\) and \(y\). Statement 1 is NOT sufficient to answer the question. Eliminate answer choices A and D. The correct answer choice is B, C, or E. Statement 2 says that \(y  x  \frac{xy}{100} = 4.5\). Note that this equation has an \(x\) term, a \(y\) term, and a term containing \(xy\). Thus, substitution will likely be possible. Divide the original expression by \(10\) to eliminate the fraction: \(\frac{10,000  100x + 100y  xy}{10} = 1,000  10x + 10y  \frac{xy}{10}\). Now factor out an additional \(10\) and reorder the terms in the expression: \(10(100 + y  x  \frac{xy}{100})\). The left side of the equation in statement 2 is contained in this expression. Thus, we know that we can find a value for the expression. Statement 2 alone provides sufficient information to answer the question. Answer: B
_________________
New to the Math Forum? Please read this: Ultimate GMAT Quantitative Megathread  All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 07 Dec 2009
Posts: 107
GMAT Date: 12032014

Re: S9503 [#permalink]
Show Tags
26 Nov 2014, 10:13
hi Bunuel,
How would one attempt the question within 2 mins. even though I got the answer It took me 4 complete minutes!!
Thanks



Intern
Joined: 05 Aug 2016
Posts: 38

Re: S9503 [#permalink]
Show Tags
14 Sep 2016, 09:42
2003 :1000 2004 : {(100x )/100}*1000=(100x)*10 2005 : {(100+y )/100}*(100x)*10
In 2005, unknown contains terms yxxy/100 Therefore, option B is sufficient



Manager
Joined: 01 Sep 2016
Posts: 118

Re: S9503 [#permalink]
Show Tags
14 Sep 2016, 11:19
tough one.not sure if I can complete this during the test Bunuel wrote: Official Solution:
We need to determine the number of incidents reported in 2005. The problem tells us that 1,000 incidents were reported in 2003. In 2004, \(x\) percent fewer incidents were reported, so \((100  x) \times 1,000\) incidents were reported. Since a percentage is equivalent to a fraction with a denominator of 100, we can express the number of incidents reported in 2004 as \(\frac{100  x}{100} \times 1,000\). In 2005, \(y\) percent more incidents were reported than in 2004. This can be expressed as \(\frac{100 + y}{100}(\frac{100  x}{100} \times 1,000)\). It is this target expression that we must find a value for.
Multiply the numerators and denominators: \(\frac{100 + y}{100}(\frac{100  x}{100} \times 1,000) = \frac{1,000(100 + y )(100  x)}{10,000}\).
Cancel 1,000 from the numerator and denominator and FOIL what remains: \(\frac{(100 + y)(100  x)}{10} = \frac{10,000  100x + 100y  xy}{10}\).
Evaluating this expression will require either solving for \(x\) and \(y\) or finding a way to substitute a number for all variable terms.
Statement 1 says that \(xy = 50\). This does not allow us to solve for either \(x\) or \(y\). We can substitute it into our target expression to get \(\frac{10,000  100x + 100y  50}{10}\), but doing so does not eliminate the need to solve for \(x\) and \(y\). Statement 1 is NOT sufficient to answer the question. Eliminate answer choices A and D. The correct answer choice is B, C, or E.
Statement 2 says that \(y  x  \frac{xy}{100} = 4.5\). Note that this equation has an \(x\) term, a \(y\) term, and a term containing \(xy\). Thus, substitution will likely be possible.
Divide the original expression by \(10\) to eliminate the fraction: \(\frac{10,000  100x + 100y  xy}{10} = 1,000  10x + 10y  \frac{xy}{10}\).
Now factor out an additional \(10\) and reorder the terms in the expression: \(10(100 + y  x  \frac{xy}{100})\).
The left side of the equation in statement 2 is contained in this expression. Thus, we know that we can find a value for the expression. Statement 2 alone provides sufficient information to answer the question.
Answer: B



Intern
Joined: 11 Oct 2016
Posts: 20
Location: Russian Federation
GPA: 3.5

Re: S9503 [#permalink]
Show Tags
07 Nov 2016, 00:51
bhatiavai wrote: hi Bunuel,
How would one attempt the question within 2 mins. even though I got the answer It took me 4 complete minutes!!
Thanks It's an old post but since i've been solving this now, maybe it will help someone... You can solve it within 2 minutes by getting the expression 1000 (100x)(100+y) which is 1000 (10000+100y100xxy) and noticing that statement 2 has the same variables in the same order with the same signs: y  x  xy/100. I think you don't need to go any further  you can already see that it has a solution.



Manager
Joined: 14 Jun 2016
Posts: 74
Location: India
WE: Engineering (Manufacturing)

Re: S9503 [#permalink]
Show Tags
01 Aug 2017, 08:09
fandango wrote: bhatiavai wrote: hi Bunuel,
How would one attempt the question within 2 mins. even though I got the answer It took me 4 complete minutes!!
Thanks It's an old post but since i've been solving this now, maybe it will help someone... You can solve it within 2 minutes by getting the expression 1000 (100x)(100+y) which is 1000 (10000+100y100xxy) and noticing that statement 2 has the same variables in the same order with the same signs: y  x  xy/100. I think you don't need to go any further  you can already see that it has a solution. We can use the formula for successive increase of x%, followed by decrease of y% is given by effective increase = xyxy/100. Hence we can estimate the ultimate value without much of calculation. Final value= Intial Value* effective increase in %
_________________
If you appreciate my post then please click +1Kudos



Intern
Joined: 24 Jul 2017
Posts: 5

Re: S9503 [#permalink]
Show Tags
06 Dec 2017, 22:03
Hi Bunuel, I solved this question in under 1:30 minutes, by: declaring (i) INSUFFICIENT  as only the value of xy is given, and by no means we can identify the separate values of x and y to find out the final value post the successive change. (ii) SUFFICIENT  just by looking at it, since the direct formula of Successive change is given with its value. My question is, was my decision to declare (i) insufficient too hasty ? And was my reasoning to it, correct ?
Please help.










