Jill alone can finish the job in 18 hours, Dan alone can

Question

Jill alone can finish the job in 18 hours, Dan alone can finish the job in 24 hours and Paul alone can finish the job 12 hours. What is the ratio of Jill doin the job alone to Dan and Paul doing the job together.
Thanks
explain please
9/4 is the answer.

gmat_march · Answer

I think there is something missingi n the question. Ratio of job done by jill to job done by dan and paul ( in 2hrs .. :?:

or ratio of time taken by jill to time taken by dan and paul ) however I solved for one hr and I get 4/9 Job done in 1 hr by J-> 1/18 D -> 1/24 P-> 1/12 d+p -> 1/24+1/12=3/24 ratio j/d+p -> (1/18) / (3/24) = 4/9

Ravshonbek · Answer

i thought so as well, but the answer is 9/4 which made me to post it here.
smth might be missing in the question. I have the same answer

thanks

Juaz · Answer

If D and P work together, they'll finish job in 8 hrs (1/12 + 1/24 = 1/8)
J finish job in 18 hrs.
Ratio of hrs taken to do job J/DP = 18/8 = 9/4

Whatever · Answer

I got into a trap and also answered 4/9. 

How to avoid such mistakes? How to decide in such questions "What is the ratio of Jill doin the job alone ..." whether to use ratio of job (to be done in 1 hour) or ration of hours that job could be done?.......

gmat_march · Answer

ratio of Jill doin the job alone to Dan and Paul doing the job together.  

 does this mean ratio of hrs taken by jill alone to dan and paul together? I think the question is incomplete.

Whatever · Answer

Basically I have the same Q.

Hayabusa · Answer

I did this in my head - Jill over the other two together - 18 hours for Jill, 8 hours for the rest or 18/8 - 9/4. How can you think otherwise??

Sumithra Sen · Answer

The question is asking to calculate ration of Jill doing the job alone / Paul and dan together... ( in terms of number of hours) 

It takes Jill 18 hours to finish 1 job

so in 1 hour - 1/ 18 of the Job can be done by her

it takes Paul 12 hours to finish 1 job

so in 1 hour - 1/ 12 of the job can be done by him

It takes dan 24 hours to do the same job

so in 1 hour - 1/ 24

rate at which both dan and Paul can do this together 

1/ 24 + 1/ 12 = 3/24 = 1/8

so they can finish in 1 hour - 1/ 8 of the job 

or 8 Hours- the entire job

Jill can do the same in 18 hours..

Ratio- 18/ 8 = 9/4

You should try and practice questions from MGMAT..regarding work /rate..
Hope this helps..

Jill alone can finish the job in 18 hours, Dan alone can

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