One night a certain hotel rented 3/4 of its rooms. including

Question

One night a certain hotel rented 3/4 of its rooms. including 2/3 of their air conditioned rooms. if 3/5 of its rooms were air conditioned, what percent of the rooms that were not rented were air conditioned?

20
33 1/3
35
40
80

please explain the logic

A. 20
B. 33 1/3
C. 35
D. 40
E. 80

Bunuel · Accepted Answer

One night a certain hotel rented 3/4 of its rooms. including 2/3 of their air conditioned rooms. if 3/5 of its rooms were air conditioned, what percent of the rooms that were not rented were air conditioned?

20
33 1/3
35
40
80

please explain the logic

A. 20
B. 33 1/3
C. 35
D. 40
E. 80

Let's consider the total number of rooms to be 100.

Since "3/5 of the rooms were air conditioned", the number of  air conditioned rooms  = 3/5*100 = 60.

Since "3/4 of the rooms were rented", the number of  rooms that were NOT rented  = 1/4*100 = 25.

Since "2/3 of the air conditioned rooms were rented", the number of  air conditioned rooms that were NOT rented  = 1/3*60 = 20.

The question asks to find what percent of the rooms that were not rented were air conditioned:

(air conditioned rooms that were NOT rented)/(rooms that were NOT rented)*100 = 20/25*100 = 4/5*100 = 80%.

Answer: E.

ezhilkumarank · Answer

The problem will be very easy to solve if you take a 2x2 matrix and work with the given data.

Given fractions - 2/3, 3/4, 3/5 -- L.C.M - 60

Rooms 
    Rented  Available  Total  
  AirCon  24 (Given 2/3 of total aircon)  12  36 (Given - 3/5 of total)  
  NonAircon  21  3  24  
  Total  45 (Given - 3/4 of total)  15  60 (Total considered)

Hence % of non-rented (available) that were aircon -- 12/15 -- 4/5 -- 80% (E).

muralimba · Answer

This can be easily solved using the matrix method
as the % is asked i can choose a good # for total rooms..let me choose 60 as all the 3 fractions given have 3,4&5 in the denominator and 60 is divisible by all thease 3 #s.

Given:
Total Rented=(60)3/4 = 45
Total AC rooms = (60)3/5 = 36
Total AC rooms rented = (36)2/3 = 24

Plug in:
 
 Rented Not-rented | 
 |
 AC 24 12 | 36
 |
 |
Non AC |
...............................................................
 45 15 | 60

qtn is what % is 12 in 15 = 1200/15 = 80%

fluke · Answer

Rooms Rented: 3/4
Rooms Not Rented: 1/4

Total AC: 3/5
AC Rented: (2/3)*(3/5) = 2/5
AC Not rented: 3/5 - 2/5 = 1/5.

% of AC that is yet to be rented per total of not rented room;

((1/5)/(1/4))*100 = (4/5)*100 = 80% of remaining(non-rented) rooms are AC.

Ans: "E"

siddhans · Answer

Can someone please explain where am i going wrong here? Let total rooms be 60 Rented rooms = 3/4 * 60 = 45 Rented AC rooms = 2/3 * 45 = 30 Total AC rooms = 3/5* 60 = 36 % Rooms that are AC and not rented = * 100 = 16 * (2/3) I am not sure where is my mistake... Can someone please correct me ???

KarishmaB · Answer

"including 2/3rd of their air conditioned rooms" implies that 2/3rd of their air conditioned rooms were a part of the rented rooms.

So if total air conditioned rooms = 36 (as found by you above), 2/3rd of these i.e. 24 of these were rented. So 12 AC rooms were rented.

Total number of rooms that were not rented = 60 - 45 = 15

So AC rooms form what percent of rooms not rented? 12/15 * 100 = 80%

PareshGmat · Answer

Refer diagram below (Solved using matrix method)
Going as per serial no (Marked in red) in the matrix

1. Let the total no of rooms = 100

2. 75% rented = 75

3. Not rented = 100-75 = 25

4.  \frac{3}{5}  th of 100 are air conditioned  = \frac{3}{5} * 100 = 60

5.  \frac{2}{3}  rd of air conditioned rooms are AC = \frac{2}{3} * 60 = 40

6. Not Rented AC rooms = 60-40 = 20

Percentage of Not rented AC rooms  = \frac{20}{25}* 100 = 80%

Answer = E

BrentGMATPrepNow · Answer

Here's a step-by-step approach using the Double Matrix method . Here, we have a population of motel rooms, and the two characteristics are: - air conditioning or no air conditioning - rented or not rented So, we can set up our matrix like this: https://i.imgur.com/T5nDgrq.png Now since we're asked to find a certain PERCENTAGE, let's choose a nice value for the total number of motel rooms. Notice that the question includes the fractions 3/4, 2/3 and 3/5. So, let's choose a number that works well with all of these fractions. Since 60 is the least common denominator of 3/4, 2/3 and 3/5, let's say that there are 60 motel rooms altogether. https://i.imgur.com/mBv4y1M.png Now that we're set up, we can use the given information to determine the number of rooms to place in each of the four boxes. If 3/5 of its rooms were air-conditioned So, 3/5 of the 60 rooms are air conditioned. 3/5 of 60 = 36, which means 36 rooms have AC and the remaining 24 rooms do not have AC... https://i.imgur.com/3GQjqCJ.png ...motel rented 3/4 of its rooms 3/4 of 60 = 45, so 45 rooms are rented and the remaining 15 rooms are not rented. https://i.imgur.com/KuINbuG.png ...a certain motel rented ....2/3 of its air-conditioned rooms So of the 36 rooms with AC, 2/3 were rented. https://i.imgur.com/eQqQRRn.png Now that we know the number of rooms in 1 box, and we know the sums of the rows and columns, we can fill in the remaining boxes. https://i.imgur.com/UHKrm7M.png Question : what percent of the rooms that were not rented were air-conditioned? There were 15 unrented rooms and 12 of them were air conditioned. 12/15 = 4/5 = 80% Answer: E This question type is VERY COMMON on the GMAT, so be sure to master the technique. To learn more about the Double Matrix Method, watch this video: https://www.youtube.com/watch?v=jK-tiBrrf04 EXTRA PRACTICE QUESTION https://www.youtube.com/watch?v=DsbPUSH_Wu4 More questions to practice with: EASY: https://gmatclub.com/forum/of-the-120-p ... 15386.html MEDIUM: https://gmatclub.com/forum/in-a-certain ... 21716.html HARD: https://gmatclub.com/forum/a-group-of-2 ... 24888.html KILLER: https://gmatclub.com/forum/a-certain-hi ... 32899.html

ScottTargetTestPrep · Answer

We can let the number of rooms = 60. (We choose this convenient number 60 because it is the least common multiple (LCM) of the denominators 3, 4, and 5.)

We see that 3/4 x 60 = 45 rooms were rented and 60 - 45 = 15 rooms were not rented.

We also see that 3/5 x 60 = 36 rooms are air conditioned, and 60 - 36 = 24 rooms are not air conditioned.

Thus, 2/3 x 36 = 24 air conditioned rooms were rented, so 36 - 24 = 12 air conditioned rooms were not rented.

Thus, the percent of rooms that were not rented were air conditioned is 12/15 = 4/5 = 80%.

Answer: E

dave13 · Answer

let total number of rooms be x total number of rented rooms \frac{3}{4} x let total number of AC rooms be y AC rented rooms \frac{2}{3} y if total number of AC rooms is \frac{3}{5} *100 = 60 then rented AC rooms is \frac{2}{3}*60= 40 60-40 = 20 Hence 20 AC rooms were not rented (perhaps air conditioning was noisy

) now since \frac{1}{4} *100 = 25 rooms were not rented then To find what percent of the rooms that were not rented were air conditioned we just divide number of AC not rented rooms by total number of not rented rooms \frac{20}{25}=0.8 i made it

!!!!!!!!!!!!!' pushpitkc , niks18 , generis is my approach correct ?

generis · Answer

dave13 , well done! Spot on. Excellent logical reasoning. +1 Hilarious aside.

P.S. I owe you answers . . . I have not forgotten . . . P.P.S. Here is how I checked your math . . . Categories, binary choices, fractions and percents? Fast check? Maxtrix! dave13matrix2.png

niks18 · Answer

Hi  dave13

generis , has already explained you the matrix method. Here's a small tip from my side - Whenever you see fractions, it's convinient to use SMART Numbers. Here Smart numbers are usually the LCM of denominators.

So we have three fractions here 3/4, 2/3, & 3/5, hence the denominators are 4, 3, 5 whose LCM is 60.

So let the total rooms be 60

So rooms rented  = \frac{3}{4}*60=45

Hence rooms not rented  = 60-45=15

Rooms with AC  =\frac{3}{5}*60=36

AC rooms rented  = \frac{2}{3}*36=24

Hence AC rooms not rented  = 36-24=12

Therefore % of rooms that were not rented and were air conditioned  = \frac{12}{15}*100 = 80 %

CrackverbalGMAT · Answer

One night a certain hotel rented 3/4 of its rooms. including 2/3 of their air conditioned rooms. if 3/5 of its rooms were air conditioned, what percent of the rooms that were not rented were air conditioned?

20
33 1/3
35
40
80

please explain the logic

let's assume that the total no of rooms in the hotel = 60 (LCM of the denominators of the fractions in the question i.e 4,3,5 = 60)

No of rooms rented = 3/4 * 60 = 45
No of air conditioned rooms = 3/5 * 60 = 36
No of air conditioned rooms rented = 2/3 * 36 = 24
No of rooms not rented= 60 - 45 = 15
No of air conditioned rooms not rented = 36-24 = 12.

Percent of the rooms that were not rented were air conditioned = 12/15 *100 = 4/5 * 100 = 80 %

Option E is the correct answer.

Thanks,
Clifin J Francis

Kinshook · Answer

Given: One night a certain hotel rented 3/4 of its rooms. including 2/3 of their air conditioned rooms.

Asked: if 3/5 of its rooms were air conditioned, what percent of the rooms that were not rented were air conditioned?

Rented   Not Rented  Total  
  Airconditioned  2y/3=24x  y/3=12x  y=(3/5)*60x =36x  
  Non Air conditioned        
  Total   (3/4)*60x = 45x  60x - 45x = 15x  60x

The percent of the rooms that were not rented were air conditioned = 12x/15x * 100% = 80%

IMO E

tryorcry · Answer

please advise, my answer is wrong and i have not read any comments before writing this so i can explain what i was thinking while solving.
let total rooms be 100 and total AC rooms be x
    
 AC rooms  
 Non AC rooms 
 Total 
 
  Rented rooms 
 2x/3 
  
 3/4*100=75 
 
  Non Rented rooms

Total 
 3/5*100=60

hence x= 60
2x/3=40 and hence AC rooms which were not rented = 60-40=20

Hence, 20% of total rooms were having AC which were not rented

Adit_ · Answer

Most people solved by taking examples. So I will try solving logically without any numbers taken as such.

2/3rd air conditioned is rented.
This directly means that remaining 1/3rd of air conditioned went where? NOT rented.

Now how many not rented? 1/4th

They say total air conditioned rooms = 3/5th

Under not rented we have 1/3rd Air conditioned room, we also know Air conditioned rooms = 3/5T.

Simply substituting:
1/3*3/5T = 1/5T. Now we know with respect to total rooms how many are air conditioned but not rented.
That is all we need!

The percent is calculated with respect to not rented = 1/4T.
Thus, 
1/5T / 1/4T =  80%

Answer:  Option E

Adit_ · Answer

You nearly got the right answer.
You should take percentage with respect to the no.of NON RENTED rooms.

20 AC rooms were not rented out of 100-75 = 25 non rented room.
So 20/25 =  80% .

One night a certain hotel rented 3/4 of its rooms. including

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Rooms
	Rented	Available	Total
AirCon	24 (Given 2/3 of total aircon)	12	36 (Given - 3/5 of total)
NonAircon	21	3	24
Total	45 (Given - 3/4 of total)	15	60 (Total considered)

	Rented	Not Rented	Total
Airconditioned	2y/3=24x	y/3=12x	y=(3/5)*60x =36x
Non Air conditioned
Total	(3/4)*60x = 45x	60x - 45x = 15x	60x

	AC rooms	Non AC rooms	Total
Rented rooms	2x/3		3/4*100=75
Non Rented rooms
Total	3/5*100=60

GMAT Problem Solving (PS) Questions

One night a certain hotel rented 3/4 of its rooms. including

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