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

 It is currently 29 May 2017, 00:22

### 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

# Some PS questions- Need explanation

Author Message
Manager
Joined: 06 Apr 2010
Posts: 145
Followers: 3

Kudos [?]: 742 [0], given: 15

Some PS questions- Need explanation [#permalink]

### Show Tags

17 Aug 2010, 06:18
Need help in explanation of following problems. Need to know how quickly we can solve such problems to save time.

3. Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 hours. S and T, working together at their respective constant rates, can do the same job in 5 hours. How many hours would it take R, working alone at its constant rate, to do the same job?
A. 8
B. 10
C. 12
D. 15
E. 20

OA E
Intern
Joined: 22 Jun 2010
Posts: 42
Followers: 0

Kudos [?]: 123 [0], given: 1

Re: Some PS questions- Need explanation [#permalink]

### Show Tags

17 Aug 2010, 09:38
udaymathapati wrote:
Need help in explanation of following problems. Need to know how quickly we can solve such problems to save time.

3. Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 hours. S and T, working together at their respective constant rates, can do the same job in 5 hours. How many hours would it take R, working alone at its constant rate, to do the same job?
A. 8
B. 10
C. 12
D. 15
E. 20

OA E

Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 ==> 1/R +1/S + 1/T = 1/4 (1)

S and T, working together at their respective constant rates, can do the same job in 5 hours

1/S + 1/T = 1/5 (2)

(1)-(2) ==> 1/R=1/5 - 1/4 = 1/20 ==> R=20

Hope it helps
Senior Manager
Status: Fighting on
Joined: 14 Mar 2010
Posts: 317
Schools: UCLA (R1 interview-WL), UNC(R2--interview-ding) Oxford(R2-Admit), Kelley (R2- Admit ), McCombs(R2)
WE 1: SE - 1
WE 2: Engineer - 3
Followers: 5

Kudos [?]: 29 [0], given: 3

Re: Some PS questions- Need explanation [#permalink]

### Show Tags

17 Aug 2010, 14:21
lets say time taken by r = r hrs
lets say time taken by s = s hrs
lets say time taken by t = t hrs

given to us = 1/r + 1/s + 1/t = 1/4 -----(1)
1/s + 1/t = 1/5 -----(2)

plug in (2) in (1)

1/5 + 1/r = 1/4

1/r = 1/20
r = 20 hrs
Intern
Joined: 11 Aug 2010
Posts: 23
Schools: SUNY at Stonyb Brook
WE 1: 4 yrs
Followers: 0

Kudos [?]: 24 [0], given: 37

Re: Some PS questions- Need explanation [#permalink]

### Show Tags

17 Aug 2010, 15:37
1/R +1/S + 1/t = 1/4

given that 1/S +1/T = 1/5

that makes it
1/R + 1/5 = 1/4
thus 1/R = 1/4 -1/5 = 5-4 /20 =1/20
hence R = 20 .

Hope this helps
_________________

Consider giving Kudos if my post helped you in some way

Re: Some PS questions- Need explanation   [#permalink] 17 Aug 2010, 15:37
Display posts from previous: Sort by