GMAT Question of the Day - Daily to your Mailbox; hard ones only

 It is currently 24 May 2019, 22:13

### 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

# A machine that produces stroopwafels operates for four hours. During t

Author Message
TAGS:

### Hide Tags

Retired Moderator
Joined: 29 Apr 2015
Posts: 837
Location: Switzerland
Concentration: Economics, Finance
Schools: LBS MIF '19
WE: Asset Management (Investment Banking)
A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

15 May 2015, 02:29
2
5
00:00

Difficulty:

65% (hard)

Question Stats:

64% (02:18) correct 36% (01:59) wrong based on 160 sessions

### HideShow timer Statistics

A machine that produces stroopwafels operates for four hours. During the first hour the machine works at a constant rate. During the next two hours, it works at double that rate, and during the last hour it works at double its previous rate. If the machine produces X stroopwafels during the three first hours, then during the four hours the machine produces how many stroopwafels?

A. 4/5X
B. 9/5X
C. 2X
D. 9/4X
E. 7/3X

_________________
Saving was yesterday, heat up the gmatclub.forum's sentiment by spending KUDOS!

PS Please send me PM if I do not respond to your question within 24 hours.
Intern
Joined: 04 May 2015
Posts: 1
WE: Information Technology (Computer Software)
Re: A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

15 May 2015, 03:48
What do you mean by - three first hours ?
e-GMAT Representative
Joined: 04 Jan 2015
Posts: 2873
Re: A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

15 May 2015, 04:31
2
Given
We are given the rates of the machines for 4 hours of its operations. We are told that if the machine produces $$x$$ stroopwafels in the first 3 hours of its operation, what would be the total stroopwafels produced by machine in 4 hours.

Approach
We know that Work = Rate * Time. Since we are given a relation between the rates of the machine during each hour and we know the time taken we can calculate the amount of work done.

Working Out
Let's assume the rate of machine in the 1st hour to be r stroopwafels/hour i.e. it can produce r stroopwafels in the first hour. So the rate of machine in the 2nd and 3rd hour would be 2r and the in the 4th hour would be 4r. Let's now find out the amount of stroopwafels produced during each hour

Stroopwafels produced in 1st hour = r * 1 = r

Stroopwafels produced in the 2nd hour = 2r * 1 = 2r

Stroopwafels produced in the 3rd hour = 2r * 1 = 2r

Stroopwafels produced in the 4th hour = 4r * 1 = 4r

We are given that amount of stroopwafels produced first three hours is $$x$$ i.e. (r +2r +2r) = 5r = $$x$$. We are asked to find the number of stroopwafels produced in four hours by the machine in terms of $$x$$ .

Since 5r = $$x$$, the amount of stroopwafels produced during the 4th hour = 4r = $$\frac{4x}{5}$$.

Therefore total stroopwafels produced in 4 hours by the machine is $$x + \frac{4x}{5} = \frac{9x}{5}$$

Hope its clear

Regards
Harsh
_________________
Current Student
Joined: 13 Nov 2014
Posts: 108
GMAT 1: 740 Q50 V40
Re: A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

15 May 2015, 07:30
reto wrote:
A machine that produces stroopwafels operates for four hours. During the first hour the machine works at a constant rate. During the next two hours, it works at double that rate, and during the last hour it works at double its previous rate. If the machine produces X stroopwafels during the three first hours, then during the four hours the machine produces how many stroopwafels?

A. 4/5X
B. 9/5X
C. 2X
D. 9/4X
E. 7/3X

Sigh. I picked A because I was solving for the ratio of the 4th hour to the first 3 hours. Reading is very important.
_________________
Gmat prep 1 600
Veritas 1 650
Veritas 2 680
Gmat prep 2 690 (48Q 37V)
Gmat prep 5 730 (47Q 42V)
Gmat prep 6 720 (48Q 41V)
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 14198
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

15 May 2015, 15:57
1
Hi reto,

This question, while wordy, is perfect for TESTing VALUES..

We're given a series of production rates for a machine. Let's TEST VALUES:

To start, let's say the machine creates 2 items/hour in the first hour.
During the next 2 hours, the rate doubles, so we have 4 items/hour for 2 hours.
Finally, during the last hour, the rate doubles again, so we have 8 items/hour for the last hour.

X is the total number of items during the first 3 hours, so X = 2+4+4 = 10 items

We're asked for the number of items made during all 4 hours (relative to the value of X); the total number of items in all 4 hours is 2+4+4+8 = 18 items.

Since the answers are all DIFFERENT fractions, each will give us a different answer when X=10....we're looking for whichever one equals 18.....

Answer B: (9/5)(10) = 18 This is a MATCH

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

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

# Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save \$75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/
VP
Joined: 07 Dec 2014
Posts: 1192
Re: A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

23 Dec 2016, 14:17
reto wrote:
A machine that produces stroopwafels operates for four hours. During the first hour the machine works at a constant rate. During the next two hours, it works at double that rate, and during the last hour it works at double its previous rate. If the machine produces X stroopwafels during the three first hours, then during the four hours the machine produces how many stroopwafels?

A. 4/5X
B. 9/5X
C. 2X
D. 9/4X
E. 7/3X

let r=initial rate
5r+4r=9r=total units produced in 4 hours
5r=x
r=x/5
substituting,
9*x/5=9x/5=total units produced in 4 hours
Non-Human User
Joined: 09 Sep 2013
Posts: 11012
Re: A machine that produces stroopwafels operates for four hours. During t  [#permalink]

### Show Tags

08 Apr 2018, 11:12
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Re: A machine that produces stroopwafels operates for four hours. During t   [#permalink] 08 Apr 2018, 11:12
Display posts from previous: Sort by

# A machine that produces stroopwafels operates for four hours. During t

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.