A qualified worker digs a well in 5 hours. He invites 2 appr

I must be totally blind! I do not see how you can get 1.4 hours out of 50/29.

Here's how I see it: each hour 29/50 of the job is completed, therefore after the first hour, 29/50 is complete and 21/50 is still remaining to be completed. 21/50 is just slightly less than 29/50, which is inline with the 1.7 that Juaz got.

Can someone please explain what I am missing?

Thanks!

50/29 = 1.7 hrs

(.7)60 = approx 40 mins

so total time = 1 hour and 40 mins.

I think the answers are a bit confusing.

Is there a fast way of calculating the time 44 mims from 21/29 hours ??

21/29 is slightly greater (~1/30) than 21/30 or 42/60 or 42 mins.

bunuel,
Is there a method( text book approach) to calculate the time 44 mims from 21/29 hours ??

21/29 th of an hour is (21/29) * (60 minutes) = ~43 minutes.

Walker gave perfect way to get approximate result here: gmat-club-test-m00-64356.html#p470808

A qualified worker digs a well in 5 hours. He invites 2 apprentices, both capable of working 3/4 as fast and 2 trainees both working 1/5 as fast as he. If the five-person team digs the same well, how much time does the team need to finish the job?

A) 1:24
B) 1:34
C) 1:44
D) 1:54
E) 2:14



I started with the original rate for the worker as 1/5.

Each apprentice would have a rate (1/5)*(3/4) = 3/20

Each trainee would have a rate (1/5) * (1/5) = 1/25

Combining all of it together 1/5 + 3/20 + 3/20 + 1/25 + 1/25 = 58/100 per hour

After one hour, the remaining work to be done is 42/100

Is it possible to use this approach to solve the problem?

I did just like you and have the same doubt.. If someone could help.

Hi,
the method is perfect, it only misses out on last step..

what you are getting 58/100 is one hour work..
so the time required will be reciprocal of this=100/58= 1 42/58, which approx equal to 1:44..

Tks for your reply!

We need to do this because of the formula: R x T = J ?

So:
(29/50) x t = 1
t = 1 / (29/50)
t = 50/29

Thats it?

Regards.

Yes, you are absolutely correct with your observation..
Moreover most of the Qs related to this aspect follow these steps..

Hi All,

These types of 'Work' questions can be solved in a couple of different ways (depending on how you want to 'organize' the rate information). It can often help to think in terms of the number of worker-hours required to complete the job.

The Qualified Worker takes 5 hours to complete a job, so the job requires 5 Worker-hours of effort to be finished.

The Qualified Worker can complete 1 Worker-hour per hour.
Each of the two apprentices can complete 3/4 of a Worker-hour per hour.
Each of the two trainees can complete 1/5 of a Worker-hour per hour.

Total = 1 + 2(3/4) + 2(1/5) = 1 + 1.5 + .4 = 2.9 Worker-hours completed per hour by this group.

Since the job requires 5 Worker-hours of effort, the total time will be...

5/2.9 hours =
50/29 hours =
1 21/29 hours

21/29 is a little more than 2/3 (since 20/30 = 2/3). Thus, we're looking for an answer that is a little more than 1 2/3 hours. There's only one answer that matches....

Final Answer:

GMAT assassins aren't born, they're made,
Rich

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.