Perry, Maria, and Lorna are painting rooms in a college dormitory.

Question

Perry, Maria, and Lorna are painting rooms in a college dormitory. Working alone, Perry can paint a standard room in 3 hours, Maria can paint a standard room in 2 hours, and Lorna can paint a standard room in 2 hours 30 minutes. Perry, Maria, and Lorna have decided that, to speed up the work, 2 of them will paint a standard room together.`

Select the value closest to the shortest time in which a 2-person team could paint a standard room, and select the value closest to the longest time in which a 2-person team could paint a standard room, with each person working at his or her respective rate. Make only two selections, one in each column.

ID: 100374

chetan2u · Accepted Answer

sthahvi

P, M and L can do the work individually in 3, 2 and 2.5 hrs.

When two of them coworkers together:

1) Least time : It will be when the two fastest work together, that is M and L.
You can work out with 1 hr work of each, which is 1/2 and 1/2.5 or 2/5
 \frac{1}{2}+\frac{2}{5}=9/10 . So they will finish the work in 10/9 hrs or 60*10/9 =200/3=66.67 minutes or 1 hr 7 mins approx.
OR
Take 10 hrs ( LCM of 2 and 2.5): In 10 hrs M can do 5 jobs at rate of 1 per 2 hr and L can do 4 at rate of 2.5 per hour.
Thus combined both do 4+5 or 9 in 10 hrs or 10/9 for 1 work.

(2) Maximum time : It will be when the two slowest work together, that is P and L.
You can work out with 1 hr work of each, which is 1/3 and 1/2.5 or 2/5
 \frac{1}{3}+\frac{2}{5}=\frac{11}{15} . So they will finish the work in 15/11 hrs or 60*15/11=5.55*15=82.5 minutes or 1 hr 22 mins approx.

minustark · Answer

Longest time will be when Perry and Lorna work : In one hour P does 1/3 of total work and L does 2/5 part. Total= 11/15. So time taken = 15/11 =1 4/11 which is around 1 hour 22 minutes.
Shortest time when Lorna and Maria work. In one hour M paints 1/2 part and L paints 2/5 part. Together in 1 hour they paint = .5 + .4 =.9 part. So to paint total work, they need = 10/9 hour =  1 1/9 hour = 1hour 7 minutes.

CAMANISHPARMAR · Answer

The shortest time is possible when Lorna and Maria work together as their speed of doing work is more. Together in 1 hour, they do 90% of the work (50%+40%). 1/0.9 = 1 hour 7 minutes.

The longest time is possible when Lorna and Perry work together as their speed of doing work is less. Together in 1 hour, they do 73.33% of the work (40%+33.33%). 1/0.7333 = 1 hour 22 minutes.

Apt0810 · Answer

The shortest time will be there when 
both Lornaa and Maria work together . So in 1 hour, they complete 90% of the work,which is 1/0.9 = 1 hour 7 minutes.

The longest time will be there when both Lorna and Perry work together. So in 1 hour, they do 73.33% of the work,which is 1/0.7333 = 1 hour 22 minutes.

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sthahvi · Answer

here I have a question how do you decide which one will take less time, calculating all will take time  minustark

chetan2u  if you could please help ? thanks

hassan233 · Answer

Let's deal with the givens first.
Let's say there are 100 units of work.
Time * rate = work done
Let P, M, L represent the individual's rate.
They are all painting the same standard room (same amount of work)
3*P = 100
2*M = 100
2.5*L = 100
Now, you can find their rate.
P = 33.3
M = 50
L = 40
Now to find the shortest time, pick the 2 fastest people, obviously, those who paint the room in less time are the fastest. Those two people are M and L.
To find the time those two people will take to paint the same standard room we will do t*M + t*L = 100
Plug and chug, t*50 + t*40 = 100
t(50+40) = 100
90t = 100
t = 100/90 hours
10/9 hours is 1 hour and 7 mins

Now to find the longest time, pick the 2 slowest people (aka the people who took the longest amount of time). Those people are P and L.
To find the time those two people will take to paint the same standard room we will do t*P + t*L = 100
33.3t + 40t = 100
t(33.3 + 40) = 100
73.3t = 100
drop the .3, it adds complication and the times between answer choice are not very close.
t = 1.37 hours which is 1 hour and 22 minutes

pranskius · Answer

Hi! Thinking of a quick way to solve this. Any thoughts on the below approach?
Shortest: 2 hours and 2.5 hours speeds: Maria's half room done in 1 hour, Lorma's half room done in 1 hour and 15 mins, but Maria will help Lorma once Maria is done, so that 15 mins timeframe is roughly split in half. Thus shortest is 1 hour + 15/2 = 1 hour and 7 mins (closest choice).

Longest: same approach: 3 hours and 2.5 hours = 1.5 hours and 1 hour 15 mins, but split remaining 15 mins in half which is roughly 7, and add to 1 hour 15 mins = 1h15m + 7 = 1h22min.

Does this approach make sense or am I setting myself up for failure? It seems intuitive to me and rather quick compared to summing up fractions.

sssaniaa · Answer

chetan2u

Thank you so much for your reply! It was helpful. Maybe I'm confused or something...but why did you flip/invert the fraction of 11/15*60 --> 15/11*60? Don't we usually do that when we divide?

Same thing happened for 1/2.5 became 2/5 -- why? Isn't it suppose to be 5/2?

chetan2u · Answer

Hi

11/15 is one hour work, that is 11/15th of the work is completed in one hour. 
=> 11/15 in 1 hour
So 1 work in 1/(11/15) hour or 15/11 hour.

That is we flip one hour or one day work to get time taken to complete the entire work.

Scholar94 · Answer

I solved this in a slightly different way

First, there are 3 unique ways by which we can match 2 of them together such that they both paint together

1.MP (Maria and Perry)
2.ML (Maria and Loma)
3.PL (Perry and Loma)

We can then find the number of time in which each of these combination could take to finish painting

Speed= 1/Time

Combined speed of each of the above combination is

MP>>1/2+1/3=5/6
ML>>1/2+2/5=9/10
PL>>1/3+2/5=11/15

Combined time (Inverse of speed):

MP>> 1 min 12 secs
ML>> 1 min 7 secs (Shortest)
PL>> 1 min 22 secs (Longest)

chini · Answer

shouldnt this question be in the math related section

bb · Answer

I would agree with you but we need to consult how Jim official guide classified this question...

Not sure if someone can doublecheck it.

Posted from my mobile device

chetan2u · Answer

Yes, it should be a math-related question.

ManifestDreamMBA · Answer

Shortest time = Fastest 2 together
Rfastest = 1/2 + 1/2.5 = 1/2 + 2/5 = 9/10
Tfastest = 10/9 = 1+1/9 hr
1/9 * 60 = 6.666 = ~7
1 hr 7mins

Fastest time = Slowest 2 together
Rslowest = 1/3 + 1/2.5 = 1/3 + 2/5 = 11/15
Tslowest = 15/11 = 1+4/11 hr
4/11 * 60 = 240/11 = 21.... = ~22
1 hr 22mins

Rickooreoisb · Answer

whenever two times are given

Combined time is 1/A+1/B=1/T (T=total time)

Simple formula is A*B/(A+B)

Plug, use calculator and solve.

Usernamevisible · Answer

In this do note that A and B are time taken and not speed

so for getting the shortest time take two faster people i.e. 2 hr and 2.5 hr 
and for longest time take two slowest people i.e. 2.5 and 3 hr as A and B respectively

Perry, Maria, and Lorna are painting rooms in a college dormitory.

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Shortest time	Longest time
		49 minutes
		1 hour 7 minutes
		1 hour 12 minutes
		1 hour 14 minutes
		1 hour 22 minutes
		1 hour 45 minutes

Shortest time	Longest time
		49 minutes
		1 hour 7 minutes
		1 hour 12 minutes
		1 hour 14 minutes
		1 hour 22 minutes
		1 hour 45 minutes

GMAT Two-part Analysis (TPA) Questions

Perry, Maria, and Lorna are painting rooms in a college dormitory.

Prep Toolkit

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My Rewards