Aptitude - Clock - Discussion

To: Nitin

You are wrong. The given answer is correct. Don't get confused.

Let me explain in simple manner:

Error Clock :: Original Clock

3 min 5 sec :: 3 min

185 sec :: 180 sec

[9 hr 15 min = 555 min = 33300 sec]

33300 sec :: (180/185 x 33300) sec

33300 sec :: 32400 sec

333000sec = 9 hrs 15 min :: 32400 sec = 9 hrs [:. 32400/3600 = 9]

So,
Time passed by Error clock = 9 hrs 15 min.
Time passed by Original clock = 9 hrs.

Therefore, 9 hrs after 7 am is 4 pm.


Note: What was wrong in Nitin's explanation?

555/3 <--- Problem is here.

It should be

555 min/3 min 5 sec [or] 33300/185

Please think twice before solve problem. Hope this will help you. All the best!

Can anyone tell the reason behind the multiplication [1/20*720/37*37/4]?

Why they are multiplying the values at last to get 9 hrs? I am confused here. Rest all is clear. Please help me.

Time from 7 a.m to 4:15 p.m = 9hr 15min.

= 9*60min+15min = 555min.

3min 5sec clock(wrong) = 3min (correct).

3*60sec+5sec = 3*60 sec.

185sec = 180sec.

If 1 sec = 180/185 sec.

Then 555 min = (180/185)*555.

= 540 min.

= 9hr.

Than correct answer is 7a.m +9hr = 4p.m.

Time between 7AM to 4.15PM = 9 hours 15 Minutes = 9+15/60 hours = 9+1/4 hours = ((9*4)+1)/4 hours = (36+1)/4 hours = 37/4 hours.

Now 3 Minutes 5 seconds of this clock = 3 minutes of the correct clock--------(1).

So, by converting above into hours we get,
First we convert into minutes,

3+5/60 = 3+1/12 = ((3*12)+1)/12 = 37/12 ---------(2).

Now we convert above result into Hours, we get 37/12*60 = 37/720 hours.

And on right side of equation 1, 3 minutes after converting into hours becomes 3/60 hours that is 1/20 hours----------(3).

So from equations 1, 2, 3 we get,
37/720 hours of this clock = 1/20 hours of correct clock.

Then 37/4 hours of this clock = (1/20)*(37/4)*(720/37) = 9 hours.
Therefore correct time is 7+9 hours = 16 Hours on 24 clock, that is 4PM on 12 hours clock.

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.

Another view can be:

In 3 minutes the error is 5 seconds, so every hour it gains 100 seconds.

Correct Clock ----------------------------> Wrong Clock
7 hrs ----------------------------> 7 hrs
8 hrs ----------------------------> 8hrs 100 sec
9 hrs ----------------------------> 9 hrs 200 sec
10 hrs ----------------------------> 10 hrs 300 sec
11 hrs ----------------------------> 11 hrs 400 sec
12 hrs ----------------------------> 12 hrs 500 sec
1 hrs ----------------------------> 1 hrs 600 sec
2 hrs ----------------------------> 2 hrs 700 sec
3 hrs ----------------------------> 3 hrs 800 sec
4 hrs ----------------------------> 4 hrs 900 sec ----> 4 hrs 15 minutes

We can also solve it by;

Time from 7 a.m to 4.15 pm is 9hrs and 15 mins.
9hrs is 540 min and 15 min=555 min.
Then, how many 3 min in 555 min=555/3=185.
So, 5 sec is added 185 times.

185*5=925 sec.925 sec can be converted into 15 min(925/60=15.4 @approx 15min).
Watch shows the time at 4:15 pm.
15 min added.so the correct time is 4 PM.

Thanks for explaining @Sundar.

How we got 37/720 ?