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

 It is currently 22 Oct 2019, 07:51

### 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

# Working at the same constant rate, 4 machines, working together, take

Author Message
TAGS:

### Hide Tags

GMAT Club Legend
Joined: 12 Sep 2015
Posts: 4017
Working at the same constant rate, 4 machines, working together, take  [#permalink]

### Show Tags

29 Dec 2016, 13:12
1
Top Contributor
6
00:00

Difficulty:

25% (medium)

Question Stats:

72% (01:30) correct 28% (01:40) wrong based on 237 sessions

### HideShow timer Statistics

Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?

A) 2
B) 4
C) 8
D) 16
E) 32

*Kudos for all correct solutions

_________________
Test confidently with gmatprepnow.com
VP
Joined: 31 Oct 2013
Posts: 1465
Concentration: Accounting, Finance
GPA: 3.68
WE: Analyst (Accounting)
Re: Working at the same constant rate, 4 machines, working together, take  [#permalink]

### Show Tags

14 Oct 2018, 06:51
4
1
GMATPrepNow wrote:
Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?

A) 2
B) 4
C) 8
D) 16
E) 32

*Kudos for all correct solutions

Important Rule:

no. of machine *rate *Time = work.

Given,

Machine = 4

Time = 8

work = 16

we can find out the rate.

4*8*r = 16

r = 1/2.

This rate can be used to 2nd case.

machine * rate * time = work

m * 1/2 * 16 = 64

m = 8.

##### General Discussion
Senior Manager
Joined: 13 Oct 2016
Posts: 359
GPA: 3.98
Re: Working at the same constant rate, 4 machines, working together, take  [#permalink]

### Show Tags

29 Dec 2016, 13:48
2
GMATPrepNow wrote:
Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?

A) 2
B) 4
C) 8
D) 16
E) 32

*Kudos for all correct solutions

4 machines working at a constant rate:

$$\frac{1}{x} + \frac{1}{x} + \frac{1}{x} + \frac{1}{x} = \frac{16}{8}$$

$$\frac{4}{x} = 2$$

$$x=2$$ (days per birdhouse) or just $$\frac{8}{4} = 2$$ (days per birdhouse)

Had the rate been kept the same we would have got 32 houses in 16 days not 64. That means we need to double the rate to fulfill this job or to double the number of machines.

y - new # of machines

$$\frac{y}{2} = 2*2$$

$$\frac{y}{2} = 4$$

$$y=8$$

Manager
Joined: 22 May 2015
Posts: 126
Re: Working at the same constant rate, 4 machines, working together, take  [#permalink]

### Show Tags

29 Dec 2016, 19:29
2
Given :4 Machines - > 8 Days -> 16 Bird Houses
Need : ___ Machines -> 16 Days -> 64 BirdHouses

From given 8 Machines - 8 Days - 32 BH
=> 16 M - 16 D - 64 BH
_________________
Consistency is the Key
GMAT Club Legend
Joined: 12 Sep 2015
Posts: 4017
Re: Working at the same constant rate, 4 machines, working together, take  [#permalink]

### Show Tags

29 Dec 2016, 20:07
Top Contributor
GMATPrepNow wrote:
Working at the same constant rate, 4 machines, working together, take 8 days to make a total of 16 birdhouses. How many such machines are required to make 64 birdhouses in 16 days?

A) 2
B) 4
C) 8
D) 16
E) 32

*Kudos for all correct solutions

Another approach is to see what the original 4 machines can do in 16 days.

4 machines take 8 days to make 16 birdhouses.
So, in 16 days, those same 4 machines can make 32 birdhouses
So, if we add an additional 4 machines (that can also make 32 birdhouses in 16 days), the 8 combined machines will make 64 birdhouses in 16 days.

_________________
Test confidently with gmatprepnow.com
Senior Manager
Joined: 03 Mar 2017
Posts: 366
Re: Working at the same constant rate, 4 machines, working together, take  [#permalink]

### Show Tags

17 Oct 2018, 11:13
4 machines, working together, take 8 days to make a total of 16 birdhouses

Therefore in 4*8-----32 mach-days=6 Birdhouses
1 Bird house=2 mach-days

Similarly 64birdhouses=64*2 mach-days
Given days 16 and we need to find number of machines m

IMO C.
_________________
--------------------------------------------------------------------------------------------------------------------------
All the Gods, All the Heavens, and All the Hells lie within you.
Re: Working at the same constant rate, 4 machines, working together, take   [#permalink] 17 Oct 2018, 11:13
Display posts from previous: Sort by