Maybe the only person authorized to run it got sick and had to leave. Maybe the cleaning lady spilled something on it.

I think this was in your experience.

it was closed down and the other two machines were left to finish the job.

That mean other machine were still running?

 

And, again, where does the 14 come from?

From 9 A.M. to TILL 11AM will make total 14 hours i though.

 

From 9 A.M. to TILL 11AM will make total 14 hours i though.

I think it is two hours. From 9-11 in the morning. Not 9-23. AM/PM is confusing.

 

From 9 A.M. to TILL 11AM will make total 14 hours i though.

From 9 in the morning until 11 in the morning. How many hours is that?

Does it make any sense for the problem to even ask something that has any of the machines shutting down in 14 hours given that any of the machines, on their own, would be long finished with the entire job by then?

 

I think this was in your experience.

????

That mean other machine were still running?

Uh... yeah.

The problem only says that machine P was shut down. There is nothing about machine Q or R stopping, is there?

 

A machine P can print one lakh books in 8 hours, machine Q can print the same number of books in 10 hours while machine R can print them in 12 hours. All the machines are started at 9 A.M. while machine P is closed at 11 A.M. and the remaining two machines complete work. Approximately at what time will the work (to print one lakh books) be finished ?

@RRITESH KAKKAR
Please note the word Approximately and the fact that 'One lakh'= 100,000 --- Pay very, very close attention to the former - you may ignore the latter for the purposes of this exercise...

So, given that P,Q,R = the fractions of the job completed per hour by the respective machines:
Clearly -- one might state the problem as: 2*(P+Q+R)+X*(Q+R)=1 ---- Specifically: 2*(1/8+1/10+1/12)+X(1/10+1/12)=1

Where: x Hours + 2 Hours = the total time to produce One lakh (i.e. 100,000) books as described...

@RRITESH KAKKAR Please don't be discouraged! IMNSHO this is a very poorly worded exercise which, IMO, calls the scholarship of the examination's preparers into question! -- Intentional obfuscation (via obscure denominations and 'approximate' results) may be acceptable for 'puzzles and games' but has no place in educational material!


Best regards
HP

 

I doubt lakh is an obscure denomination in India.

Approximations have to be dealt with all the time. One of the problems that is very commonly seen around here is people coming up with answers that have 32 digits after the decimal point merely because that is what their calculator displays.

 

I doubt lakh is an obscure denomination in India.

Approximations have to be dealt with all the time. One of the problems that is very commonly seen around here is people coming up with answers that have 32 digits after the decimal point merely because that is what their calculator displays.

Fair enough -- Nonetheless, I feel the 'sneaky' delivery of the problem was 'mean spirited' -- Challenging the student is one thing -- dispiriting same is quite another

I doubt lakh is an obscure denomination in India.

I wouldn't have been any happier with 'Dozen' or 'Score' in this context...

Approximations have to be dealt with all the time.

Absolutely! -- My point is merely that concepts should be introduced (even if only by category) prior to drill...

Again, I am not and do not claim to be an educator -- still...

Very best regards
HP

 

Well...

--If 'A' completes 80% of the job in 20 days then clearly 'A' would complete the entire job in 25 days...
--When 'B' joins the task 1/5 of the work remains...

Hence (A's 3_day contribution (i.e. 3/25 of the job) + B's 3_day contribution (i.e. 3/x of the job) = the fraction of the job remaining (i.e. 1/5) = 3/25+3/x = 1/5 (Where x = Days required for 'B' alone to perform the entire task...

3/25+3/x = 1/5
3/x=1/5-3/25
x=37.5days

Correct! -- But again - Please refrain from general use of decimal expansions!

 

But aren't these questions from an aptitude test (or practice tests for same)? If so, then it would seem that questions making a whole array of various assumptions about the test taker's knowledge and skill should be included if there is any hope of determining the test taker's aptitude. As one of my profs uses to say, an exam is a poor exam if anyone scores 100% because it has failed to measure just how much that person really knows. Similarly, an exam is a poor exam if anyone scores 0% because it has failed to measure just how much that person really doesn't know.

 

But aren't these questions from an aptitude test (or practice tests for same)? If so, then it would seem that questions making a whole array of various assumptions about the test taker's knowledge and skill should be included if there is any hope of determining the test taker's aptitude. As one of my profs uses to say, an exam is a poor exam if anyone scores 100% because it has failed to measure just how much that person really knows. Similarly, an exam is a poor exam if anyone scores 0% because it has failed to measure just how much that person really doesn't know.

That's an excellent point! -- Owing to intent, an aptitude test might (and should) be expected to differ from a textbook 'problem set'... I only hope that @RRITESH KAKKAR recognizes the fact that he is being generally 'tested' as well as specifically instructed...

Very best regards
HP

 

@RRITESH KAKKAR

Here's something slightly different -- Please rest assured that you have demonstrated the requisite skills!

Two cars are traveling at 60 mph and 45 mph respectively. If the faster car travels two hours longer and twice as far, then:
What are the distances traveled by each car?
What are the operation times of each car?

Hint 1: Although I am not insisting up on it, simultaneous solution of multiple equations will significantly simplify matters.
Hint 2: Having solved for any one of the unknowns, the solution of the remaining three is simple arithmetic --- Literally!

@RRITESH KAKKAR

I'm going to ask that you make an extra effort on this one!!! -- I've been way too liberal with 'sledgehammer hints' as of late (Owing -- could it be? -- to that Santa cap sported by my Avatar)

Best regards
HP

 

Try to work it symbolically until the last lines. Use the following:

Car A:
Ra = speed of Car A = 60 mph
Da = distance traveled by Car A
Ta = operation time for Car A

Car B:
Rb = speed of Car B = 45 mph
Db = distance traveled by Car B
Tb = operation time for Car B

Then Td = 2 hr for the difference in operating time for the two cars.

Get your answers purely in terms of the above symbols:

Da = ....
Ta = ....

Db = ....
Tb = ....

Only THEN plug in the numbers (WITH UNITS!!!!) to get the final results.

Finally, verify that your answers satisfy the problem constraints.

 

Yeah, but notice that they don't believe in following their own rules. As is often the case with EE and ME texts, they really only give lip service to units and believe that just tacking the units that you want the result to have onto the end is sufficient. Just look at their work on the top of page 32.

Good catch. I just looked at the list. ...Happened on to it by chance when thumbing through a $1 used book I bought.

 

Good catch. I just looked at the list. ...Happened on to it by chance when thumbing through a $1 used book I bought.

I think there list is a pretty good one. I'd have to go back and really look at it in detail, but I didn't see anything that I have a big objection to or that really needs to be added. What I found surprising is that several of their rules for how to layout your work mirror the homework format guidelines that I've used (and held as requirements in my courses) for a couple decades. But maybe it isn't so surprising since I learned those guidelines from the CE (Statics, in particular) course I took as an undergrad and I'm sure they didn't come out of thin air there.

One thing I am finding increasingly is that students just flat refuse to follow the guidelines, no matter how many points they lose as a result. I don't understand it -- except that now if a students feels that they don't see a need for something, then they don't believe they should have to do it and will simply complain to the Dean if they lose points as a result. A lot of whiney babies these days, to be sure.

 

A machine P can print one lakh books in 8 hours, machine Q can print the same number of books in 10 hours while machine R can print them in 12 hours. All the machines are started at 9 A.M. while machine P is closed at 11 A.M. and the remaining two machines complete work. Approximately at what time will the work (to print one lakh books) be finished ?

So, given that P,Q,R = the fractions of the job completed per hour by the respective machines:
Clearly -- one might state the problem as: 2*(P+Q+R)+X*(Q+R)=1 ---- Specifically: 2*(1/8+1/10+1/12)+X(1/10+1/12)=1

Where: x Hours + 2 Hours = the total time to produce One lakh (i.e. 100,000) books as described...

x=2.091+2=4

 

Two cars are traveling at 60 mph and 45 mph respectively. If the faster car travels two hours longer and twice as far, then:
What are the distances traveled by each car?
What are the operation times of each car?

Car A:
Ra = speed of Car A = 60 mph
Da = distance traveled by Car A
Ta = operation time for Car A

Car B:
Rb = speed of Car B = 45 mph
Db = distance traveled by Car B
Tb = operation time for Car B

Then Td = 2 hr for the difference in operating time for the two cars.

Get your answers purely in terms of the above symbols:

Da = ....
Ta = ....

Db = ....
Tb = ....



no idea how o start.

 

So, given that P,Q,R = the fractions of the job completed per hour by the respective machines:
Clearly -- one might state the problem as: 2*(P+Q+R)+X*(Q+R)=1 ---- Specifically: 2*(1/8+1/10+1/12)+X(1/10+1/12)=1

Where: x Hours + 2 Hours = the total time to produce One lakh (i.e. 100,000) books as described...

x=2.091+2=4

@RRITESH KAKKAR
1) I've twice requested that you refrain form expression of nonintegral values as decimal expansions! -- Now I'm going to insist!
2) "=" means: "is equal to" whereas "~" means: "is approximately equal to"

Please state your results properly -- bearing notes 1 and 2 (above) in mind...K?

 

1) I've twice requested that you refrain form expression of nonintegral values as decimal expansions! -- Now I'm going to insist!
2) "=" means: "is equal to" whereas "~" means: "is approximately equal to"

Sorry, i did not get your point.

x=2.091=~2hours
Total time taken is 4 Hours i.e, 1PM

 

Total time taken is 4 Hours

Incorrect! The total time taken is approximately 4 hours (Specifically 4+1/11 hours)
Hence:
Time required ~ 4 hours -- ergo completion time ~ 1:00 PM (note: "≅" and "≈" likewise indicate approximation)

x=2.09

"2.09" is a decimal expansion -- and, as such, is inelegant (at best) and, often, (as in this case), imprecise -- Please state nonintegral values properly! -- I don't know how else to say it???

Best regards
HP