Aptitude - Clock - Discussion

925/60 is not equal to 15, it is equal to 15 5/12 and you subtracted the 15 min but what about 25 sec? Please explain.

3 min = 3+ 5/60 min = 3+1/12 = 37/12 min.

quarter past = 15 min.

7am-4:15pm = 9hr 15 min= 9 x 60+15=555min.
for 37/12 min = 3 min,
for 555min = ?
540min.

540/60 = 9hr,
7am + 9h = 4pm.

If the clock gains 5sec for every 3mins it travels 9hrs and 15mins i.e., 9.25hrs.
Let the actual clock goes 'x' 3mins.

Then the clock which gains 5 secs for every 3 mins will go (3mins)x + (5secs)x =9.25hrs
=> (3+ (5/60))x = 9.25*60.
So x= 180mins,
i.e., x=3hrs,
So the actual clock goes 3x i.e., 9hrs.
So, 9hrs from 7 a.m. is 4 p.m.

Watch gain 5 sec each 3min.

1-hour watch gain 100sec.

100x9 =900 further 15 min watch gain 25sec if we divided 925/60 we get 15 min we minus 15 min from 4.15 we get 4.00.

Thank you everyone for explaining the answer.

It gains 5 seconds in 3 minutes.

3min = 5seconds
3min = 1/12 min
1min = 1/36 min

Let correct watch shows time which is x min ahead of 7 am.

Then minutes gained by faulty clock = x/36minutes.

So, the faulty clock is ahead of 7 am by (x + x/36)min or 37x/36 min.

but in question, it is given faulty clock shows 4.15 pm which is (9*60+15)min or 555min ahead of 7 am.

So,
37x/36 = 555

x = 540min or 9 hrs

So, the correct time is 7 am + 9hr = 4 pm.

Note: We have to calculate the time gained by the faulty clock in terms of the correct clock not in terms of the faulty clock time given in the question

Crt time: 3mins wrong time: 3mins 5 seconds.
So 1 hr = 1hr 100 seconds wrong time.
7:00 Am to 4:15 PM = 9 hrs 15 mins difference,
For 9 hr 15 mins = 9 hr 925 sec wrong time,
Subtract 925 sec (900sec = 15 mins)from 4: 15 PM

So, the ANSWER is 4:00 PM.

THE CORRECT ANSWER IS OPTION(A)

Step 1: Find total gain per minute

Given: 5 sec gain in 3 min
Gain per minute = 5/3 sec

Step 2: Find total time shown by watch
From 7:00 a.m. to 4:15 p.m. = 555 minutes

Step 3: Find total gain in that time,
Total gain = 555 × 5/3.
= 925 sec.

Convert:
925 sec = 15 min 25 sec.

Step 4: Subtract gain from shown time,

Watch is fast, so:
Real time=4:15−15 min 25 sec.
= 3:59:35 p.m.
converting to mixed fraction give us answer as 3:59:35/60 that is equals to 3:59:7/12.

Clock gains 5 seconds every 3 minutes = 100 seconds every hour (60 minutes) = 900 seconds every 9 hours = 15 minutes every 9 hours.

Hence, when the faulty clock shows 4:15 PM, the actual clock should show 15 minutes less i.e. 4:00 PM.

@All.

To those who say option A is correct.

1. Total minutes as per the time shown by the watch from 7.00 am to 4.15 pm
555 minutes.
(these 555 minutes also include the 5 sec. gained by the watch every 3 minutes.
Most people have failed to adjust to the same.)

2. Let's see how to adjust to nullify the 5 seconds gained every three minutes to arrive at the correct answer.
Every three minutes, the watch gains 5 seconds.
3 minutes = 180 seconds.
So, 555minutes * 180/185 =540 minutes.

NOTE: This step can be solved in many different ways. for eg, instead of converting 3 minutes in 180 seconds, you can keep them as it is and instead say gains per minute is 1.66666667 seconds. etc.

3. Final answer 7.00 am + 540 minutes = 4.00 pm.