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clock problem

by hemant_rajput » Fri Jan 18, 2013 9:03 am
Q7 . A clock is set right at 12 noon on Monday. It looses 1/2% on the correct time in the first week but gains 1/4% on the true time during the second week. The time show on Monday after two week will be
a. 12:25:12
b. 11:34:48
c. 12:50:24
d. 12:24:16
e. None of these
[spoiler]oa:a[/spoiler]
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by jkaustubh » Fri Jan 18, 2013 10:30 am
Are you sure that this question is a real GMAT question.

Well the correct answer is obviously A, as the clock will gain 0.42 hours during the two weeks. Now converting the 0.42 hours into minutes we get 25 minutes approximately, hence the correct answer is A.

In my opinion, question of such magnitude wont be asked in GMAT, though this can/ may be a survey question.

cheers
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by GMATGuruNY » Fri Jan 18, 2013 11:26 am
hemant_rajput wrote:Q7 . A clock is set right at 12 noon on Monday. It looses 1/2% on the correct time in the first week but gains 1/4% on the true time during the second week. The time show on Monday after two week will be
a. 12:25:12
b. 11:34:48
c. 12:50:24
d. 12:24:16
e. None of these
[spoiler]oa:a[/spoiler]
The number of hours in a week = 24*7 = 168.

Week 1: The clock loses (1/2)% of the actual time
To LOSE time is to OVERCOUNT the number of hours.
Let's say that we must leave a party at 2pm.
if the clock overcounts the number of hours and reads 2pm when the time is really 1pm, we will leave 1 hour EARLIER than is necessary, with the result that we LOSE one hour of party time.
Here, the number of hours OVERCOUNTED = (1/2)/100 * 168 = 84/100 = .84 hours.
Thus, at the end of week 1, the clock is AHEAD .84 hours.

Week 2: The clock gains (1/4)% of the actual time
To GAIN time is to UNDERCOUNT the number of hours.
Let's say we that we must leave a party at 2pm.
If the clock undercounts the number of hours and reads 1pm when the time is really 2pm, we will leave the party 1 hour LATER than is necessary, with the result that we GAIN one hour of party time.
Here, the number of hours UNDERCOUNTED = (1/4)/100 * 168 = 42/100 = .42 hours.
In other words, the clock MOVES BACK .42 hours.

Net change for the two weeks = .84 - .42 = .42 hours.

Since 1 hour = 60 minutes, we get:
(1 hour)/(60 minutes) = (.42 hours)/(x minutes)
x = .42(60) = 25.2 minutes = 25 minutes, 12 seconds.

Since the clock is AHEAD by 25 minutes, 12 seconds, the time shown = 12:25:12.

The correct answer is A.
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by hemant_rajput » Sat Jan 19, 2013 8:48 am
jkaustubh wrote:Are you sure that this question is a real GMAT question.

Well the correct answer is obviously A, as the clock will gain 0.42 hours during the two weeks. Now converting the 0.42 hours into minutes we get 25 minutes approximately, hence the correct answer is A.

In my opinion, question of such magnitude wont be asked in GMAT, though this can/ may be a survey question.

cheers
Actually it is not but I don't see any reason why it can't be.

Using Guru's method it can be done in say 30 sec.

Also one more point, we don't need to do calculation for 1st and 2nd week separately. We can say that in 1st week clock is loosing the 1/2% in first week but we are gaining 1/4% in second week. So in actual we are loosing 1/4% week.

As "Guru" already show the rest of the calculation. I think it won't be long that you come up with answer, isn't it.
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by jkaustubh » Sat Jan 19, 2013 10:17 am
hemant_rajput wrote:
jkaustubh wrote:Are you sure that this question is a real GMAT question.

Well the correct answer is obviously A, as the clock will gain 0.42 hours during the two weeks. Now converting the 0.42 hours into minutes we get 25 minutes approximately, hence the correct answer is A.

In my opinion, question of such magnitude wont be asked in GMAT, though this can/ may be a survey question.

cheers
Actually it is not but I don't see any reason why it can't be.

Using Guru's method it can be done in say 30 sec.

Also one more point, we don't need to do calculation for 1st and 2nd week separately. We can say that in 1st week clock is loosing the 1/2% in first week but we are gaining 1/4% in second week. So in actual we are loosing 1/4% week.

As "Guru" already show the rest of the calculation. I think it won't be long that you come up with answer, isn't it.
Dear Hemant Ji,

I guess you did not read my answer in totality, I also solved your question, arriving at the same OA that was the first option, though I did not explain like "Guru".

Also I would like to add, that the clock gains not loses 0.42 hours during the two weeks.

Regards
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by hemant_rajput » Sun Jan 20, 2013 4:18 am
jkaustubh wrote:
hemant_rajput wrote:
jkaustubh wrote:Are you sure that this question is a real GMAT question.

Well the correct answer is obviously A, as the clock will gain 0.42 hours during the two weeks. Now converting the 0.42 hours into minutes we get 25 minutes approximately, hence the correct answer is A.

In my opinion, question of such magnitude wont be asked in GMAT, though this can/ may be a survey question.

cheers
Actually it is not but I don't see any reason why it can't be.

Using Guru's method it can be done in say 30 sec.

Also one more point, we don't need to do calculation for 1st and 2nd week separately. We can say that in 1st week clock is loosing the 1/2% in first week but we are gaining 1/4% in second week. So in actual we are loosing 1/4% week.

As "Guru" already show the rest of the calculation. I think it won't be long that you come up with answer, isn't it.
Dear Hemant Ji,

I guess you did not read my answer in totality, I also solved your question, arriving at the same OA that was the first option, though I did not explain like "Guru".

Also I would like to add, that the clock gains not loses 0.42 hours during the two weeks.

Regards

oops, sorry my bad:-)
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by BTG14 » Fri Jan 25, 2013 8:03 pm
Thanks guru for you explanation. Still i am not clear with gaining part.. I feel it should be lose not gain.. Please can anybody explain it one more time clearly...
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by ceilidh.erickson » Sat Jan 26, 2013 8:05 am
hemant_rajput wrote: Actually it is not but I don't see any reason why it can't be.
There are several reasons why this can't be an official GMAT problem. The wording is awkward and at times even grammatically incorrect! "Set right" does not necessarily mean the same thing as "set to the correct time." The question then alternates between "correct time" and "true time," which a GMAT problem would never do. "Time show," "looses" and "two week" are grammatically incorrect... it's unclear whether this was retyped incorrectly, or if this is a problem with the original.

The larger problem is that there are ambiguities in the actual math. It's unclear is "1/2%" means (1/2)% or 1/(2%). It's also unclear what "loosing [sic] a % on the time" actually means. A real GMAT problem would be much more explicit - e.g. loses a certain percent of minutes every hour.

These critiques may seem irrelevant - "hey, I'm still just practicing math skills" - but they're not. Practicing with poorly worded problems can actually be detrimental to your process. You need to train yourself to be very attentive to subtleties of language in quant problems, and you can't by practicing problems like these.

See Ron's explanation here for more: https://www.beatthegmat.com/a-man-travel ... tml#561729
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by prakash mali » Tue May 19, 2015 1:36 am
I think so, sir, answer is B.
Because I have a one Question...in that.
There is option
A) 11:25:12
B) 11:34:48
C) 11:09:36
D) none of these..
Explanation..
When it loses 1/2% on correct time in first week.
This means it reduce the time with 0.84 hours..
And when it gains 1/4% on the true time during second week.
It means it increase the time with 0.42 hours.
So actually it reduces with 0.42 hours.that means it reduce with 25 minutes and 12 seconds.
So answer is 11:34:48.

Is it correct or incorrect?
Please reply.
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by prakash mali » Tue May 19, 2015 1:36 am
I think so, sir, answer is B.
Because I have a one Question...in that.
There is option
A) 11:25:12
B) 11:34:48
C) 11:09:36
D) none of these..
Explanation..
When it loses 1/2% on correct time in first week.
This means it reduce the time with 0.84 hours..
And when it gains 1/4% on the true time during second week.
It means it increase the time with 0.42 hours.
So actually it reduces with 0.42 hours.that means it reduce with 25 minutes and 12 seconds.
So answer is 11:34:48.

Is it correct or incorrect?
Please reply.
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by GMATGuruNY » Tue May 19, 2015 6:02 am
The prompt is ambiguously worded.
It is unclear what is meant by the clock loses time and the clock gains time.
In my solution above, I assume that to lose time is to overcount the number of hours and that to gain time is to undercount the number of hours.
Other readers might interpret just the opposite:
that to lose time is to undercount the number of hours, while to gain time is to overcount the number of hours.
As Ceilidh has suggested, I would ignore this problem.
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