December 15, 2018 December 15, 2018 07:00 AM PST 09:00 AM PST Aiming to score 760+? Attend this FREE session to learn how to Define your GMAT Strategy, Create your Study Plan and Master the Core Skills to excel on the GMAT. December 15, 2018 December 15, 2018 10:00 PM PST 11:00 PM PST Get the complete Official GMAT Exam Pack collection worth $100 with the 3 Month Pack ($299)
Author 
Message 
TAGS:

Hide Tags

Math Expert
Joined: 02 Sep 2009
Posts: 51218

Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
06 Oct 2014, 08:17
Question Stats:
79% (01:22) correct 21% (01:26) wrong based on 267 sessions
HideShow timer Statistics
Tough and Tricky questions: Word Problems. Wes works at a science lab that conducts experiments on bacteria. The population of the bacteria multiplies at a constant rate, and his job is to notate the population of a certain group of bacteria each hour. At 1 p.m. on a certain day, he noted that the population was 2,000 and then he left the lab. He returned in time to take a reading at 4 p.m., by which point the population had grown to 250,000. Now he has to fill in the missing data for 2 p.m. and 3 p.m. What was the population at 3 p.m.? A. 50,000 B. 62,500 C. 65,000 D. 86,666 E. 125,000
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
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




Senior Manager
Joined: 13 Jun 2013
Posts: 275

Re: Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
06 Oct 2014, 11:07
Bunuel wrote: Tough and Tricky questions: Word Problems. Wes works at a science lab that conducts experiments on bacteria. The population of the bacteria multiplies at a constant rate, and his job is to notate the population of a certain group of bacteria each hour. At 1 p.m. on a certain day, he noted that the population was 2,000 and then he left the lab. He returned in time to take a reading at 4 p.m., by which point the population had grown to 250,000. Now he has to fill in the missing data for 2 p.m. and 3 p.m. What was the population at 3 p.m.? A. 50,000 B. 62,500 C. 65,000 D. 86,666 E. 125,000 let the rate be x, then population of the bacteria after each hour can be given as 2000, 2000x, 2000(x^2), 2000(x^3) now population at 4pm =250,000 thus we have 2000(x^3) = 250,000 thus x=5 therefore population at 3pm = 2000(25) = 50,000




SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1825
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)

Re: Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
06 Oct 2014, 21:23
1 AM ................. 2000 Let the rate of growth = x 2 AM ....................... 2000x 3 AM ......................... \(2000 x^2\) 4 AM ......................... \(2000 x^3\) Given that \(2000 x^3 = 250000\) x = 5 at 3 AM \(= 2000 * 5^2 = 50000\) Answer = A
_________________
Kindly press "+1 Kudos" to appreciate



Director
Status: Professional GMAT Tutor
Affiliations: AB, cum laude, Harvard University (Class of '02)
Joined: 10 Jul 2015
Posts: 671
Location: United States (CA)
Age: 39
GMAT 1: 770 Q47 V48 GMAT 2: 730 Q44 V47 GMAT 3: 750 Q50 V42
WE: Education (Education)

Re: Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
17 Mar 2016, 15:09
Here is a handwritten solution to the question. You could either use the algebraic equation, or try the answers to see which one works.
Attachments
Screen Shot 20160317 at 4.03.05 PM.png [ 185.19 KiB  Viewed 3800 times ]
_________________
Harvard grad and 99% GMAT scorer, offering expert, private GMAT tutoring and coaching worldwide since 2002.
One of the only known humans to have taken the GMAT 5 times and scored in the 700s every time (700, 710, 730, 750, 770), including verified section scores of Q50 / V47, as well as personal bests of 8/8 IR (2 times), 6/6 AWA (4 times), 50/51Q and 48/51V (1 question wrong).
You can download my official testtaker score report (all scores within the last 5 years) directly from the Pearson Vue website: https://tinyurl.com/y94hlarr Date of Birth: 09 December 1979.
GMAT Action Plan and Free EBook  McElroy Tutoring
Contact: mcelroy@post.harvard.edu (I do not respond to PMs on GMAT Club.)
...or find me on Reddit: http://www.reddit.com/r/GMATpreparation



Senior SC Moderator
Joined: 22 May 2016
Posts: 2210

Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
20 Jul 2017, 11:35
Bunuel wrote: Tough and Tricky questions: Word Problems. Wes works at a science lab that conducts experiments on bacteria. The population of the bacteria multiplies at a constant rate, and his job is to notate the population of a certain group of bacteria each hour. At 1 p.m. on a certain day, he noted that the population was 2,000 and then he left the lab. He returned in time to take a reading at 4 p.m., by which point the population had grown to 250,000. Now he has to fill in the missing data for 2 p.m. and 3 p.m. What was the population at 3 p.m.? A. 50,000 B. 62,500 C. 65,000 D. 86,666 E. 125,000 I worked from the answer choices because finding the constant rate looked quick for four of the answers. It was quick. If we have 1 p.m.  2,000 2 p.m.  ??? 3 p.m.  ??? 4 p.m.  250,000 Then because the answer choices are for 3 p.m., divide 4 p.m. amount by an answer choice to get the multiplication factor. Use that factor: divide the 3 p.m. amount by the factor to get the 2 p.m. amount, then once more (2 p.m. amt / factor = 1 p.m. amt) to see whether the answer matches 2,000. 1. I started with (C) where 3 p.m. amount is 125,000 \(\frac{250,000}{125,000}\) to get multiplication factor = 2 3:00 > 2:00 is \(\frac{125,000}{2}\) = 62,500 at 2:00. Stop. Much too big. The next step, \(\frac{65,000}{2}\) is not going to equal 2,000 at 1 p.m. 2. Try A, where 3 p.m. amount = 50,000 \(\frac{250,000}{50,000}\) = multiplication factor 5Hour between 2:00 and 3:00 is then \(\frac{50,000}{5}\) = 10,000 at 2:00 2:00 > 1:00 is \(\frac{10,000}{5}\) = 2,000 at 1 p.m. Correct Answer A



Manager
Joined: 21 Jul 2017
Posts: 193
Location: India
Concentration: Social Entrepreneurship, Leadership
GPA: 4
WE: Project Management (Education)

Re: Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
11 Apr 2018, 10:22
Ouch this hurts... Read the question twice..thrice and every time saw 1000 instead of 2000



Manager
Joined: 19 Jun 2017
Posts: 54
Location: India
GPA: 3.23

Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
10 May 2018, 03:56
Bunuel Why can't we use the ARITHMETIC PROGRESSION FORMULA as the bacteria is multiplying at a constant rate? I tried it but I got 86666 as the answer. Any help would be appreciated. Thanks in advance.



Math Expert
Joined: 02 Sep 2009
Posts: 51218

Re: Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
10 May 2018, 22:28



Intern
Joined: 26 Mar 2018
Posts: 2

Wes works at a science lab that conducts experiments on bacteria. The
[#permalink]
Show Tags
15 May 2018, 19:04
simple approach this problem:
First, we take out the last 3 zeros for simplicity's sake.
hr 1 = 2 hr 2 = unknown hr 3 = unknown hr 4 = 250
Since we know that it is growing at a constant rate, we could assume that there is a patter between the four numbers. Next we look at 250 and see its factors. 250 = 2 x 5 x 5 x 5 < notice that there is a 2 here and 3 five's. If the number is growing at a constant rate, then we could plug in the only difference here  the five's
hr 1 = 2 hr 2 = 2 x 5 hr 3 = 2 x 5 x 5 = 50,000 (don't forget the zeros we took out in the beginning) hr 4 = 2 x 5 x 5 x 5
Answer is A




Wes works at a science lab that conducts experiments on bacteria. The &nbs
[#permalink]
15 May 2018, 19:04






