Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 26 May 2017, 03:38

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# At his regular hourly rate, Don had estimated the labour cos

Author Message
TAGS:

### Hide Tags

Senior Manager
Affiliations: UWC
Joined: 09 May 2012
Posts: 393
GMAT 1: 620 Q42 V33
GMAT 2: 680 Q44 V38
GPA: 3.43
WE: Engineering (Entertainment and Sports)
Followers: 31

Kudos [?]: 1283 [5] , given: 100

At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

31 Jul 2012, 10:01
5
KUDOS
70
This post was
BOOKMARKED
00:00

Difficulty:

85% (hard)

Question Stats:

62% (04:01) correct 38% (03:35) wrong based on 1394 sessions

### HideShow timer Statistics

At his regular hourly rate, Don had estimated the labour cost of a repair job as $336 and he was paid that amount. However, the job took 4 hours longer than he had estimated and, consequently, he earned$2 per hour less than his regular hourly rate. What was the time Don had estimated for the job, in hours?

(A) 28
(B) 24
(C) 16
(D) 14
(E) 12
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 38894
Followers: 7737

Kudos [?]: 106181 [21] , given: 11608

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

31 Jul 2012, 10:21
21
KUDOS
Expert's post
20
This post was
BOOKMARKED
macjas wrote:
At his regular hourly rate, Don had estimated the labour cost of a repair job as $336 and he was paid that amount. However, the job took 4 hours longer than he had estimated and, consequently, he earned$2 per hour less than his regular hourly rate. What was the time Don had estimated for the job, in hours?

(A) 28
(B) 24
(C) 16
(D) 14
(E) 12

Say the regular hourly rate was $$r$$$and estimated time was $$t$$ hours, then we would have: $$rt=336$$ and $$(r-2)(t+4)=336$$; So, $$(r-2)(t+4)=rt$$ --> $$rt+4r-2t-8=rt$$ --> $$t=2r-4$$. Now, plug answer choices for $$t$$ and get $$r$$. The pair which will give the product of 336 will be the correct answer. Answer B fits: if $$t=24$$ then $$r=14$$ --> $$rt=14*24=336$$. Answer: B. Hope it's clear. _________________ Intern Joined: 01 Jan 2011 Posts: 21 Location: Kansas, USA Schools: INSEAD, Wharton Followers: 3 Kudos [?]: 19 [11] , given: 9 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 01 Aug 2012, 10:39 11 This post received KUDOS 1 This post was BOOKMARKED [336][/X] - [336][/(X+4)]= 2 Solve for X. Ans= 24 since -28 is not a valid answer. Intern Joined: 26 Sep 2012 Posts: 17 Followers: 0 Kudos [?]: 15 [0], given: 1 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 07 Dec 2012, 03:03 I have just worked on OG Math practice questions and hardly have I solved this question. That's why I have used Google and found you guys sayak636 wrote: [336][/X] - [336][/(X+4)]= 2 I have composed the same equation, however its solving has taken me for ages. I like Bunuel's solution, but I has not guessed to do the same. I'd only slightly change the course of solving. When we get to $$t = 2r - 4$$, $$r$$ easily seems to be replaced by $$336/t$$. Now we have $$t = (2*336/t) - 4$$ and can plug answer choices to find out the correct option. Intern Joined: 07 Feb 2013 Posts: 13 GMAT 1: 650 Q48 V32 GMAT 2: 730 Q49 V41 WE: Engineering (Other) Followers: 0 Kudos [?]: 20 [1] , given: 9 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 15 Jun 2013, 20:41 1 This post received KUDOS 1 This post was BOOKMARKED While substitution does tend to take long for this problem, before substitution you could factorize 336 to its primes = 2*2*2*2*3*7 Now you can begin to substitute : Ans Choice A = 28*12 (2*2*7*2*2*3) not equal to 32*10 (clearly its 320 and not 336) Choice B = 24*14 (2*2*2*3*2*7) equals 28*12 (from prev choice) thx Verbal Forum Moderator Joined: 10 Oct 2012 Posts: 629 Followers: 83 Kudos [?]: 1193 [1] , given: 136 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 16 Jun 2013, 04:50 1 This post received KUDOS 4 This post was BOOKMARKED Shiv636 wrote: [336][/X] - [336][/(X+4)]= 2 Solve for X. Ans= 24 since -28 is not a valid answer. Infact, one doesn't need to solve after this step too: $$\frac{336}{x} - \frac{336}{(x+4)} = 2$$ 336[(x+4)-x] = 2*x(x+4) x(x+4) = 672 From the given options, we can straightaway eliminate A and C, as because the units digit after multiplication of 28*(28+4) and 16*(16+4) will never be 2. We also know that 14*20 = 280 and 12*20 = 240. Thus, 14*18(D) or 12*16(E) can never equal 672. By eliminaion, the answer is B. _________________ Intern Joined: 16 Oct 2013 Posts: 4 Followers: 0 Kudos [?]: 0 [0], given: 0 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 07 Jan 2014, 08:41 Bunuel wrote: macjas wrote: At his regular hourly rate, Don had estimated the labour cost of a repair job as$336 and he was paid that amount. However, the job took 4 hours longer than he had estimated and, consequently, he earned $2 per hour less than his regular hourly rate. What was the time Don had estimated for the job, in hours? (A) 28 (B) 24 (C) 16 (D) 14 (E) 12 Say the regular hourly rate was $$r$$$ and estimated time was $$t$$ hours, then we would have:

$$rt=336$$ and $$(r-2)(t+4)=336$$;

So, $$(r-2)(t+4)=rt$$ --> $$rt+4r-2t-8=rt$$ --> $$t=2r-4$$.

Now, plug answer choices for $$t$$ and get $$r$$. The pair which will give the product of 336 will be the correct answer.

Answer B fits: if $$t=24$$ then $$r=14$$ --> $$rt=14*24=336$$.

Hope it's clear.

On my own I got to the step where I need to utilize the answer choices. I didn't know what to do at that point because it never crosses my mind to use the answer choices and backwards solve like this.

I've only ever seen this kind of method recommended when the problem involves second degree equations. Is that a fair statement? You only backwards solve like this when dealing with second degree equations?
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7376
Location: Pune, India
Followers: 2288

Kudos [?]: 15116 [6] , given: 224

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

07 Jan 2014, 22:38
6
KUDOS
Expert's post
12
This post was
BOOKMARKED
Rdotyung wrote:
Bunuel wrote:
macjas wrote:
At his regular hourly rate, Don had estimated the labour cost of a repair job as $336 and he was paid that amount. However, the job took 4 hours longer than he had estimated and, consequently, he earned$2 per hour less than his regular hourly rate. What was the time Don had estimated for the job, in hours?

(A) 28
(B) 24
(C) 16
(D) 14
(E) 12

On my own I got to the step where I need to utilize the answer choices. I didn't know what to do at that point because it never crosses my mind to use the answer choices and backwards solve like this.

I've only ever seen this kind of method recommended when the problem involves second degree equations. Is that a fair statement? You only backwards solve like this when dealing with second degree equations?

You utilize the answer choices whenever you CAN. Here I would keep an eye on the choices right from the start. I would say
R*T = 336 (his regular hourly rate * time he estimated)
The options give us the value of T which is an integer.

$$336 = 2^4*3*7$$

So R*T = 336
(R-2)*(T + 4) = 336
So T as well as T+4 should be factors of 336.
If T is 28, T+4 is 32 which is not a factor of 336 so ignore it.
If T is 24, T+4 is 28. Both are factors of 336. Keep it. If T is 24, R is 14. So (R - 2) is 12. 12*28 does gives us 336 so T = 24 must be the correct answer.

But note that if you want to reduce your mechanical work, you need to be fast in your calculations. You cannot spend a minute working on every option or making calculation mistakes.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Intern Joined: 13 Feb 2014 Posts: 7 Followers: 0 Kudos [?]: 0 [0], given: 9 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 23 Apr 2014, 08:06 How do you go from > 336[(x+4)-x] = 2*x(x+4) to > x(x+4) = 672? Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7376 Location: Pune, India Followers: 2288 Kudos [?]: 15116 [3] , given: 224 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 23 Apr 2014, 20:02 3 This post received KUDOS Expert's post gciftci wrote: How do you go from > 336[(x+4)-x] = 2*x(x+4) to > x(x+4) = 672? $$336 * [(x+4)-x] = 2 * x * (x+4)$$ $$336 * [x+4 -x] = 2 * x * (x+4)$$ x and -x get cancelled to give: $$336 * [4] = 2 * x * (x+4)$$ Divide both sides by 2. $$336 * 2 = x * (x+4)$$ $$672 = x * (x+4)$$ _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

Veritas Prep Reviews

Senior Manager
Joined: 29 Oct 2013
Posts: 296
Concentration: Finance
GPA: 3.7
WE: Corporate Finance (Retail Banking)
Followers: 16

Kudos [?]: 415 [1] , given: 197

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

27 May 2014, 10:12
1
KUDOS
VeritasPrepKarishma wrote:

On my own I got to the step where I need to utilize the answer choices. I didn't know what to do at that point because it never crosses my mind to use the answer choices and backwards solve like this.

I've only ever seen this kind of method recommended when the problem involves second degree equations. Is that a fair statement? You only backwards solve like this when dealing with second degree equations?
[/quote]

You utilize the answer choices whenever you CAN. Here I would keep an eye on the choices right from the start. I would say
R*T = 336 (his regular hourly rate * time he estimated)
The options give us the value of T which is an integer.

$$336 = 2^4*3*7$$

So R*T = 336
(R-2)*(T + 4) = 336
So T as well as T+4 should be factors of 336.
If T is 28, T+4 is 32 which is not a factor of 336 so ignore it.
If T is 24, T+4 is 28. Both are factors of 336. Keep it. If T is 24, R is 14. So (R - 2) is 12. 12*28 does gives us 336 so T = 24 must be the correct answer.

But note that if you want to reduce your mechanical work, you need to be fast in your calculations. You cannot spend a minute working on every option or making calculation mistakes.[/quote]

Hi Karishma, Why do T and T+4 have to be factors of 336? Why cannot rate be a fraction and difference of two fractions can yield an integer in this case 2? What am I missing here? Thanks!
_________________

My journey V46 and 750 -> http://gmatclub.com/forum/my-journey-to-46-on-verbal-750overall-171722.html#p1367876

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7376
Location: Pune, India
Followers: 2288

Kudos [?]: 15116 [3] , given: 224

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

27 May 2014, 21:56
3
KUDOS
Expert's post
1
This post was
BOOKMARKED
MensaNumber wrote:

Hi Karishma, Why do T and T+4 have to be factors of 336? Why cannot rate be a fraction and difference of two fractions can yield an integer in this case 2? What am I missing here? Thanks!

All the options are integers so value of T must be an integer. So T+4 must be an integer too. Therefore, T and T+4 must be factors of 336. Also, in GMAT, usually numbers are easy since you do not get calculators. So very rarely will you find that rate or time is a fraction. Even if it will be, it will be a simple fraction such as 1/2 etc.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Senior Manager Joined: 29 Oct 2013 Posts: 296 Concentration: Finance GPA: 3.7 WE: Corporate Finance (Retail Banking) Followers: 16 Kudos [?]: 415 [0], given: 197 Re: At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 28 May 2014, 02:22 Karishma, Thanks for your reply. Yeah that makes sense. _________________ Please contact me for super inexpensive quality private tutoring My journey V46 and 750 -> http://gmatclub.com/forum/my-journey-to-46-on-verbal-750overall-171722.html#p1367876 Current Student Status: Eagles Become Vultures Joined: 19 Jun 2014 Posts: 63 Concentration: Finance, Strategy Schools: LBS '18 (M) GMAT 1: 710 Q48 V39 GPA: 4 WE: Corporate Finance (Energy and Utilities) Followers: 0 Kudos [?]: 19 [0], given: 13 At his regular hourly rate, Don had estimated the labour cos [#permalink] ### Show Tags 07 Jan 2015, 13:51 Let t be the hourly rate and p the price: t * p =$336

Additional 4 hours and $2 less per hour would yield: (t+4) * (p-2) =$336

Since both equations are equal:

336 : p = (336 : (p-2))-4

Solving for p yields 14 (the other solution is negative, so we do not consider it)

At this point probably we are very pressed on time, so the shortcut is to find the answer the last digit of which multiplied by 4 yields 6. 14 squared is not 336 so by elimination it is 24

Senior Manager
Status: Math is psycho-logical
Joined: 07 Apr 2014
Posts: 441
Location: Netherlands
GMAT Date: 02-11-2015
WE: Psychology and Counseling (Other)
Followers: 2

Kudos [?]: 122 [1] , given: 169

At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

18 Jan 2015, 10:05
1
KUDOS
I back solved this one like this:

I started with option A, but I will only show the correct option, which is B:

I said that r*t=336, so the amount of hours he worked times the money he got for each hour should be his final salary.
Then I substituted the proposed times for t:
r*24=336
r=14 --> This is how much he should have got per hour worked.

But he worked 4 hours more, so 24+2 = 28. Then he actually got 336/28 = 12, per hour.

12 is 2 less than 14, as it is supposed to, so the correct answer is ANS B.
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 9120
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 445

Kudos [?]: 2873 [2] , given: 169

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

20 Apr 2015, 18:48
2
KUDOS
Expert's post
Hi RussianDude,

You're not expected to answer every question in the Quant section in under 2 minutes, so if you took a little longer than that on this question, then that's fine (as long as you were doing work and not staring at the screen). If you took more than 3 minutes to answer this question, then chances are that YOUR approach is the "long" approach and that you have to practice other tactics.

Here, since the answer choices ARE numbers, we're really looking for an answer that divides into 336 AND when you add 4 to that answer, that sum ALSO divides evenly into 336. The difference between those two rates should be $2 (as the question states). In that way, you can answer this question with some basic division and note-taking (and likely save time and avoid a long-winded Algebra approach). GMAT assassins aren't born, they're made, Rich _________________ 760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

60-point improvement guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Director
Joined: 07 Aug 2011
Posts: 579
GMAT 1: 630 Q49 V27
Followers: 3

Kudos [?]: 449 [1] , given: 75

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

20 Apr 2015, 22:06
1
KUDOS
macjas wrote:
At his regular hourly rate, Don had estimated the labour cost of a repair job as $336 and he was paid that amount. However, the job took 4 hours longer than he had estimated and, consequently, he earned$2 per hour less than his regular hourly rate. What was the time Don had estimated for the job, in hours?

(A) 28
(B) 24
(C) 16
(D) 14
(E) 12

$$\frac{336}{X} = \frac{336}{X+4}+2$$

X=24
_________________

Thanks,
Lucky

_______________________________________________________
Kindly press the to appreciate my post !!

Director
Joined: 10 Mar 2013
Posts: 597
Location: Germany
Concentration: Finance, Entrepreneurship
GMAT 1: 580 Q46 V24
GPA: 3.88
WE: Information Technology (Consulting)
Followers: 17

Kudos [?]: 356 [0], given: 200

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

26 Jul 2015, 09:05
t(t+4)=672
we can estimate here 20*30=600 --> 22*30=660 So we see that only A or B can be the answer here... 24*28 suits better (22*30)

A bit too large numbers to calculate, not really a GMAT Style, though it's an official GMAT Question.......
_________________

When you’re up, your friends know who you are. When you’re down, you know who your friends are.

800Score ONLY QUANT CAT1 51, CAT2 50, CAT3 50
GMAT PREP 670
MGMAT CAT 630
KAPLAN CAT 660

Math Forum Moderator
Joined: 20 Mar 2014
Posts: 2644
Concentration: Finance, Strategy
Schools: Kellogg '18 (M)
GMAT 1: 750 Q49 V44
GPA: 3.7
WE: Engineering (Aerospace and Defense)
Followers: 128

Kudos [?]: 1473 [0], given: 789

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

26 Jul 2015, 11:50
BrainLab wrote:
t(t+4)=672
we can estimate here 20*30=600 --> 22*30=660 So we see that only A or B can be the answer here... 24*28 suits better (22*30)

A bit too large numbers to calculate, not really a GMAT Style, though it's an official GMAT Question.......

An easier and more straightforward way to look at it will be:

Let T be the total hours initially calculated.

Thus per the question:

$$\frac{336}{T} - \frac{336}{T+4} = 2$$ (DO NOT solve the equation for T). Plug in the values from the options to arrive at the answer. Start with C (you can easily eliminate this as T+4 =20 and this will give a fractional value for 336/20). Then move onto B or D. If you choose D, the difference of the LHS = 7 (not equal to 2 ) and thus you can eliminate D,E as well. Finally, when you come to B, you will see that the equation is satisfied and is thus the answer.

In GMAT, if you end up calculating nasty numbers, then usually you missed out on a simple trick to reduce the effort.
_________________

Thursday with Ron updated list as of July 1st, 2015: http://gmatclub.com/forum/consolidated-thursday-with-ron-list-for-all-the-sections-201006.html#p1544515
Inequalities tips: http://gmatclub.com/forum/inequalities-tips-and-hints-175001.html
Debrief, 650 to 750: http://gmatclub.com/forum/650-to-750-a-10-month-journey-to-the-score-203190.html

Senior Manager
Joined: 11 Nov 2014
Posts: 370
Location: India
WE: Project Management (Telecommunications)
Followers: 2

Kudos [?]: 30 [0], given: 17

Re: At his regular hourly rate, Don had estimated the labour cos [#permalink]

### Show Tags

08 Oct 2015, 00:02
Can someone correct me?

336=xh
h=336/x

(h+4)=336/2x
xh+4x=168
4x=168-336
x=42

Re: At his regular hourly rate, Don had estimated the labour cos   [#permalink] 08 Oct 2015, 00:02

Go to page    1   2    Next  [ 36 posts ]

Similar topics Replies Last post
Similar
Topics:
3 At a certain company, Annie’s hourly rate is 50 percent greater than 3 29 Apr 2017, 05:27
1 The basic hourly rate for a weekly paid worker is €6 and any hours abo 1 11 Mar 2016, 06:06
11 A contractor estimated that his 10-man crew could complete 15 13 May 2017, 07:27
8 A contractor estimated that his 10-man crew could complete t 9 03 Jun 2016, 06:44
34 Alan’s regular hourly wage is 1.5 times Barney’s regular 15 24 Jan 2017, 07:52
Display posts from previous: Sort by