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23 Nov 2017, 20:03
Spongebob02 wrote: Bunuel wrote: Official Solution:
The population of Linterhast was 3,600 people in 1990 and 4,800 people in 1993. If the population growth rate per thousand is constant, then what will be the population in 1996?
A. 6,000 B. 6,400 C. 7,200 D. 8,000 E. 9,600
This is a set rate problem. If the population grew by 1,200 people in the past three years, then it grew by 33 percent: \(\frac{48003600}{3600} = \frac{1200}{3600} = \frac{1}{3} \approx 33%\) Therefore in the next three years the population will grow at the same rate of 33% because the growth rate has been constant. \(4,800 + \frac{1}{3}*4,800 = 4,800 + 1,600 = 6,400\) Another approach is to backsolve by comparing the ratio of each answer to 4,800. For example, the ratio of 7,200 to 4,800 is not the same as the ratio of 4,800 to 3,600.
Answer: B \(4,800 + \frac{1}{3}*4,800 = 4,800 + 1,600 = 6,400\) I did not understand this equation ? Sent from my Redmi 3S using GMAT Club Forum mobile appIn three years from 1990 to 1993 the population grew by third. Since the growth rate is constant, then in the next three years, from 1993 to 1996, the population will also grow by third. Hope it's clear.
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Re: M0109
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03 Dec 2017, 15:28
Spongebob02Quote: \(4,800 + \frac{1}{3}*4,800 = 4,800 + 1,600 = 6,400\) I did not understand this equation ? We have simply converted decimal (0.33%) in to fraction (1/3) for ease of calculations while dealing with fractions. Hope this helps!
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19 Dec 2017, 23:06
For me this was easier and quicker to solve using the ratios given in the question stem:
4800/3600 = x/4800 x = 6400



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19 Dec 2017, 23:16
Easy question if ever comes up on GMAT: We can see every 3 population grew up by 1 unit. Divide by 400 We get the ratio 9:12 Next equivalent ratio should be (12*4)/3=16 So, 16*400=6400 Sent from my ZUK Z2132 using GMAT Club Forum mobile app



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26 Mar 2018, 09:25
I think this is a highquality question and I agree with explanation.
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07 Jun 2018, 00:56
I think this is a highquality question and I agree with explanation.



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18 Jun 2018, 09:32
I think this is a poorquality question and I don't agree with the explanation. Hi, well the rate per year comes to be (48003600)/3 = 400/year, therefore increasing at a const. rate of 400/year, the population in 1996 should be 400/year * 3 + 4800 = 6000. Well, i agree that the OA must be 'B'. But please help me to convince myself to the OA. What made you consider the % instead ?
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18 Jun 2018, 09:47
honcho11 wrote: I think this is a poorquality question and I don't agree with the explanation. Hi, well the rate per year comes to be (48003600)/3 = 400/year, therefore increasing at a const. rate of 400/year, the population in 1996 should be 400/year * 3 + 4800 = 6000. Well, i agree that the OA must be 'B'. But please help me to convince myself to the OA. What made you consider the % instead ? Hi honcho11check your calculation in the highlighted part. also you can check an alternate approach mentioned in the below link for clarity https://gmatclub.com/forum/m01183520.html#p1770983



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Hi Bunuel, Is there any difference between "growth rate is constant" and "growth rate per 1000 is constant" ? If yes, can you please provide any simple example on how it's works out differently? I guess they both mean the same only but I'm not completely sure if that's true or if I've made any mistake below. growth rate is (48003600 )/ 3600 X 100 = 33.33% growth rate per year = 33.33 % / 3 = 11.11 % AND growth rate per thousand per year is ((4.8  3.6) / 3.6 X 100 ) /3 = 33.33% / 3 = 11.11% Also, here the time period before and after is 3. Let's say if for the same data if we'd to compute the population in 1997, how would you solve it? I tried and I get 3600 ( 10/9)^7 which is clearly wrong because 3600( 10/9)^3 is not equal to 4800. What's the mistake here? Seeing the explanation of the unitary method should help understand the original question and it's solution in a much more better way. This is good question and particularly confusing if someone is reading it for the first time. Thanks.



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23 Jun 2018, 05:20
sanjay1810 wrote: Hi Bunuel, Is there any difference between "growth rate is constant" and "growth rate per 1000 is constant" ? If yes, can you please provide any simple example on how it's works out differently? I guess they both mean the same only but I'm not completely sure if that's true or if I've made any mistake below. growth rate is (48003600 )/ 3600 X 100 = 33.33% growth rate per year = 33.33 % / 3 = 11.11 % AND growth rate per thousand per year is ((4.8  3.6) / 3.6 X 100 ) /3 = 33.33% / 3 = 11.11% Also, here the time period before and after is 3. Let's say if for the same data if we'd to compute the population in 1997, how would you solve it? I tried and I get 3600 ( 10/9)^7 which is clearly wrong because 3600( 10/9)^3 is not equal to 4800. What's the mistake here? Seeing the explanation of the unitary method should help understand the original question and it's solution in a much more better way. This is good question and particularly confusing if someone is reading it for the first time. Thanks. 1. If the growth rate is constant, then it's constant for any period of time. 2. The growth rate per 3 years is 1 + 1/3 = 4/3, so per year it's x^3 = 4/3 > \(x = \sqrt[3]{\frac{4}{3}}\) 3. In 1993, the population would be \(3,600*(\sqrt[3]{\frac{4}{3}})^3 = 4,800\) 4. In 1997, the population would be \(3,600*(\sqrt[3]{\frac{4}{3}})^7 \approx 7,044\) Hope it helps.
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Re: M0109
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23 Jun 2018, 05:35
Bunuel wrote: sanjay1810 wrote: Hi Bunuel, Is there any difference between "growth rate is constant" and "growth rate per 1000 is constant" ? If yes, can you please provide any simple example on how it's works out differently? I guess they both mean the same only but I'm not completely sure if that's true or if I've made any mistake below. growth rate is (48003600 )/ 3600 X 100 = 33.33% growth rate per year = 33.33 % / 3 = 11.11 % AND growth rate per thousand per year is ((4.8  3.6) / 3.6 X 100 ) /3 = 33.33% / 3 = 11.11% Also, here the time period before and after is 3. Let's say if for the same data if we'd to compute the population in 1997, how would you solve it? I tried and I get 3600 ( 10/9)^7 which is clearly wrong because 3600( 10/9)^3 is not equal to 4800. What's the mistake here? Seeing the explanation of the unitary method should help understand the original question and it's solution in a much more better way. This is good question and particularly confusing if someone is reading it for the first time. Thanks. 1. If the growth rate is constant, then it's constant for any period of time. 2. The growth rate per 3 years is 1 + 1/3 = 4/3, so per year it's x^3 = 4/3 > \(x = \sqrt[3]{\frac{4}{3}}\) 3. In 1993, the population would be \(3,600*(\sqrt[3]{\frac{4}{3}})^3 = 4,800\) 4. In 1997, the population would be \(3,600*(\sqrt[3]{\frac{4}{3}})^7 \approx 7,044\) Hope it helps. Thanks Bunuel. Your explanations are always very helpful. Last thing, just to confirm there is no difference between "growth rate is constant" and "growth rate per 1000 is constant", correct?



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Re: M0109
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23 Jun 2018, 05:38
sanjay1810 wrote: Bunuel wrote: sanjay1810 wrote: Hi Bunuel, Is there any difference between "growth rate is constant" and "growth rate per 1000 is constant" ? If yes, can you please provide any simple example on how it's works out differently? I guess they both mean the same only but I'm not completely sure if that's true or if I've made any mistake below. growth rate is (48003600 )/ 3600 X 100 = 33.33% growth rate per year = 33.33 % / 3 = 11.11 % AND growth rate per thousand per year is ((4.8  3.6) / 3.6 X 100 ) /3 = 33.33% / 3 = 11.11% Also, here the time period before and after is 3. Let's say if for the same data if we'd to compute the population in 1997, how would you solve it? I tried and I get 3600 ( 10/9)^7 which is clearly wrong because 3600( 10/9)^3 is not equal to 4800. What's the mistake here? Seeing the explanation of the unitary method should help understand the original question and it's solution in a much more better way. This is good question and particularly confusing if someone is reading it for the first time. Thanks. 1. If the growth rate is constant, then it's constant for any period of time. 2. The growth rate per 3 years is 1 + 1/3 = 4/3, so per year it's x^3 = 4/3 > \(x = \sqrt[3]{\frac{4}{3}}\) 3. In 1993, the population would be \(3,600*(\sqrt[3]{\frac{4}{3}})^3 = 4,800\) 4. In 1997, the population would be \(3,600*(\sqrt[3]{\frac{4}{3}})^7 \approx 7,044\) Hope it helps. Thanks Bunuel. Your explanations are always very helpful. Last thing, just to confirm there is no difference between "growth rate is constant" and "growth rate per 1000 is constant", correct? ____________________ Right.
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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.
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Re: M0109
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03 Oct 2018, 01:49
Bunuel I still don't understand what it means by growth rate per 1000 is constant. I did understand how to do the question, but I didn't understand what the literal translation of this sentence is.
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23 Oct 2018, 07:15
Hi, Please explain how do we calculate the same for say 1997 ?



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04 Nov 2018, 05:51
Bunuel wrote: mallika123 wrote: I think this is a highquality question. my issue with the explanation is that i agree to the way it is explained but i m not fully convinced that this clears my doubt about why this question is solved in this particular manner.. i solved like this and want to know why my approach is wrong 48003600=1200/3=400 1990=3600 1991=3600+400=4000 1992=4000+400=4400 1993=4400+400=4800 (now when the rate is same for each year so i did this) 1994=4800+400=5200 1995=5200+400=5600 1996=5600+400=6000 according to this method i got 6000 as an answer please help me understand why i m wring what i m basically missing out...please explain We are told that the population growth rate per thousand is constant, not that the population growth number is constant per year. Bunnel/VeritasKarishma Can you please explain what is the meaning of ..population growth per thousand vs rate of population growth The question doesn't ask for an increase by percentage rate. The question asks for an increase based on the "growth rate per thousands." I don't know what this means. I thought it was asking for the rate of population increase, which is 400 people per year (1990>1993 is an increase of 1200 people). At 400 people per year, the answer would be 6000. I had a feeling this question was too easy... Please help!!







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