One machine, working at a constant rate, can fill a certain production

Question

One machine, working at a constant rate, can fill a certain production order in 8 hours. How long would it take four identical machines, working at the same constant rate, to fill the order?

A. 2 hours
B. 4 hours
C. 8 hours
D. 16 hours
E. 32 hours

spc11 · Answer

Work done in 8 hrs = 1
Work done in 1 hr = 1/8

Work done by 4 machines in 1 hr = 1/2
So full work will be done in 2 hrs.

Ans is option A

Sent from my A0001 using  GMAT Club Forum mobile app

benejo · Answer

R * T = W
1 machine 1/8
4 machines 4 * 1/8 = 1/2

Work(4 machines)=1/2*t=1
t=2

(A)

pushpitkc · Answer

If the total production order is  32 units , 
one machine(time taken: 8 hours) will do the work at  4 units/hour .

4 such machines, working at the same constant rate, will do 16 units of work in an hour.

Therefore, the times taken by the four machines to fill the order is  \frac{32}{16} = 2 hours(Option A)

seed · Answer

8 hrs for 1 unit of work(by single machine.)
1 hr for 1/8 unit of work(by single machine.)

1 machine 1/8 of work.
4 machines 4*(1/8) work=1/2 work. Hence, (A) it will take 2 hrs for 4 identical machines.

generis · Answer

Modify   RT = W  . Add one variable to LHS. 
Manipulate it the same way.

Let  N  = Number of machines or workers
Modified formula:  N*R*T = W 
(N*R*T=W table makes this way easy to see)

Scenario 1: 
One machine can finish the work in 8 hours
 W = 1  job
 T = 8  hours

Standard formula to find individual rate:  RT=W  
Rate of one machine,  R=\frac{W}{T} 
 R = \frac{1}{8}

Scenario 2: 
At that rate, how long will it take 4 machines to finish W? 
 N = 4, R = \frac{1}{8}, W = 1  
 N*R*T=W . So

T = \frac{W}{(N*R)}

T =\frac{1}{(4*\frac{1}{8})}

T=\frac{1}{(\frac{4}{8})}=\frac{1}{(\frac{1}{2})}=1*\frac{2}{1}=2  hours

Answer A

gmatexam439 · Answer

Straight 2 .....

Use unitary method to solve such questions:

1 machine ----------- 8 hours 
4 machines ------------ 8/4 = 2 hours !

Ans = A

JeffTargetTestPrep · Answer

Since the rate of one machine is 1/8, the rate of four machines is 4 x 1/8 = 1/2.

So it would take four machines 1/(1/2) = 2 hours to complete the order.

Answer: A

One machine, working at a constant rate, can fill a certain production

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards

GMAT Problem Solving (PS) Questions

One machine, working at a constant rate, can fill a certain production

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards