Aptitude - Clock - Discussion

Actually Sundar's explanation is correct.

Don't get confusion. The question is about two clocks (accurate clock and the error clock). So many of you confused.. 59 7/12 past 3 is wrong because, you are considering only one clock.. you went wrong while dividing 555 minute by 3.. in reality... 555 minutes are passed in ERROR CLOCK,

So you must divide 555 by 3 min 5 seconds (OR 555*60=33300 seconds divided by 3*60+5=185 seconds) Then you will get the right answer.

Total hours between 7 a.m to 4.15 p.m is 9 hrs 15 min.

3 min gains 5 seconds.
15 min gains 25 seconds.
60 min gains 100 seconds.
i.e. 1 hour gains 100 seconds.
i.e. 9 hours gains 900 seconds.
i.e. 9 hours 15 min gains 900+25 = 925 seconds.
Now, 9 hours 15 min = 33300 seconds.

The correct time is = 33300 - 925 = 32375 seconds.
= 32375/3600 .
= 8.99 hr = 9 hr.

Therefore the correct time is 4 p.m.

@Dedeepya.

We can't go with the process you suggested because;

Let us take the correct time be 'x'.
Now as we already know that 'x' will be lesser than 4 : 15.
Now the mistake in your idea is you are taking x as 4:15 which means in another (4 : 15 - x) the error clock will gain (4 : 15 - x) * 3s, which you are not considering.

Kindly take 'x' instead of 4 : 15 and solve again you will definitely land into a correct answer.

FAULT CLOCK CORRECT CLOCK

7am < ---------------- > 7am
8am 100 sec < ------------ > 8am
9am 200 sec < ------------ > 9am

So on..

4pm 900 sec < ------------ > 4pm

So 4pm 900 sec = 4pm 900/60 min = 4pm 15 min.

Therefore when Fault clock shows the time 4pm 15 min the Correct clock will show 4pm.

So correct answer is 4pm.

From 7 am to 4 pm, We are getting 900 sec gain, which is 900/60 = 15 min gain.

Now, the question has asked what will be the actual time when it is showing 4:15 pm.

Now, at 4 pm it already has gained 15 min, i.e. it is showing 4:15 pm already.

I was doing it wrong when I took 900 + 25 sec, where 25 sec was for 4 to 4:15 pm, which is wrong.

We are not asked to calculate time at 4:15 pm, we are asked for 4 pm.

The answer is A.

A lot of people are ignoring the extra 25 seconds.
The exact time gained is 925 seconds.
(This is best explained in the comment down below)
900 seconds is 15 minutes. So, we deduct 15 minutes from the time given.
ADDITIONALLY, 25 seconds also will be deducted -
60 - 25 = 35 seconds remaining.
Hence, 35/60 which explains the extra 7/12.

The final answer is -> 59 7/12 minutes past 3.

For 3 mins 5 sec gain.

i.e for 180 sec clock shows 185 sec.

That means for every hour it's shows 1 min 40 sec more than actual time.

We need to calculate actual time when clock shows 4:15 pm.

Given that time set at 7 am so the difference between 7 to 4:15 is 9:15 hours.

Clock showing us 1 min 40 secs more for every hour then for 9 hours 15 secs it shows 15 mins fast.

So the answer is 4 pm.

7am to 4.15pm.
Total 9hrs 15min.

Total time in min= 9*60+15=555min.
For every three min, 5 seconds will be added to the wrong clock
555min /3min= 185 times

So total second added 185*5=925sec,
now convert 925sec to min=925/60= 15 min 25 sec,
so the time in original clock will be 4pm.
555min-15min, =540min=9hrs.
25 sec is neglected because clocks trigger by 5sec only after completing 3mins.

@Aishwarya.

You don't get confused, first calculate how many minutes are there.

9hrs * 60 minutes +15 = 555 minutes.

Again calculate how many 3 minutes are there i.e. 555 ÷ 3 =183.
Again 180 minutes * 5 second = 915.
Again 914 ÷ 60 = 15 minutes. So 4 : 15 - 15 = 4pm.

Don't bother about the remaining 15 sec because we calculate ahead of the 15 minutes, so it's very factual to deduct.

7am to 4:15====>is 9hrs and 15 min.

3min ====EXCEEDS===> 5sec.

15min==============> 25sec equation (1).

1hr (60min) =========> 100sec.

====================

======So on=========

====================

9hr=================> 900sec equation (2).

9:15 == equation(1)+equation(2) => 925 sec i.e. in 9:15 min time exceeded by 15 min.

Therefore time is 4 pm and not 4:15.