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Today is 2 March, 2 0 1 2 . My friend asked me when was the last show of Dragon Ball Z telecast. He wanted to watch the next show.
I replied that it was telecast 8 0 0 hours 4 8 0 minutes and 5 4 0 0 seconds ago and the next episode is telecast after 1010 hours of the previous one.
It was 4:00 PM when I told him the telecast time.
What will be the time and date when he should turn on the television to watch the next show ?
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An equivalent approach is to convert everything in terms of hours first before we begin calculations of time.
8 0 0 hrs 4 8 0 min 5 4 0 0 sec = 8 0 9 . 5 hrs ≡ ( − 6 . 5 ) hrs ( m o d 2 4 )
As we're working backward in time, we add the absolute value of the residue obtained to our current time and then add the 1 0 1 0 hrs m o d 2 4 to obtain time of telecast as follows:
4 : 0 0 PM ⟶ + 6 . 5 hrs 1 0 : 3 0 PM ⟶ + ( 1 0 1 0 hrs ) m o d 2 4 1 2 : 3 0 AM
Now, comes the date. We first have 8 0 9 . 5 = 8 1 6 − 6 . 5 . Since 4 : 0 0 PM and 1 0 : 3 0 PM comes in a single day after 6 . 5 hrs, we have the day of last episode as 2 4 8 1 6 = 3 4 days before current day. Working from current day, we have,
3 4 days = ( index on March 1 2 ) + ( index on Feb 1 29 ) + ( index on Jan 1 31 ) − ( current index to final day 28 )
Hence, the last telecast was on 2 8 th Jan ′ 2 0 1 5 at 1 0 : 3 0 PM . Now, we calculate day-hour increments after 1 0 1 0 hrs as follows:
1 0 1 0 hrs = 2 4 1 0 0 8 days + 2 hrs = 4 2 days + 2 hrs
Working from day of last telecast, we have,
4 2 days = ( going to Feb 1 3 ) + ( going to March 1 29 ) + ( date reached 10 )
This gives us 1 0 : 3 0 PM of 1 0 th March ′ 2 0 1 5 . We still have to add the remaining 2 hrs. Since we have new day after 1 2 : 0 0 AM and the final time we get for next telecast is 1 2 : 3 0 AM , we add another day to our obtained date.
This gives us the date of 1 1 th March ′ 2 0 1 5 and time of 1 2 : 3 0 AM as date and time of next telecast.
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ah.. its a very nice and systematic solution.
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It is almost equivalent to yours though. By the way, I noticed that I forgot to upvote your solution earlier. Well, better late than never. :)
By the way, there's are minor typos in few lines of your solution (mostly L A T E X problems). I suggest you edit them properly to make your solution cleaner.
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Initial date: 2 March,2012.
Let us first check if it is a leap year.
We know, if [ Y E A R ] ≡ 0 ( m o d 4 ) , then it is a leap year. So, 2012 is a leap year.
Number of hours to be deducted = 8 0 0
8 0 0 ≡ 8 ( m o d 2 4 )
OR
8 0 0 = 2 4 × 3 3 + 8
So, Number of days to be deducted = 3 3
Number of hours to be further deducted = 8 0 0 − 2 4 × 3 3 = 8
Number of minutes to be deducted = 4 8 0
4 8 0 m i n s = 6 0 4 8 0 h o u r s = 8 h o u r s
Number of seconds to be deducted = 5 4 0 0
5 4 0 0 s e c = 3 6 0 0 5 4 0 0 h o u r s = 1 . 5 h o u r s
So, total number of hours to be further deducted = 8 + 8 + 1 . 5 = 1 7 . 5
Now, 3 3 = 2 + 2 9 + 3 1 − 2 8
Therefore, after deducting 3 3 days the date and time would be 4 : 0 0 P M of 28 January,2012 (Since the time remains same if we deduct 24 hours)
Further deducting 1 7 . 5 h o u r s we get 1 0 : 3 0 P M of 28 January,2012
Now we have to add 1 0 1 0 h o u r s
Following the similar pattern, 1 0 1 0 ≡ 2 ( m o d 2 4 )
Number of days to be added = 4 2
Number of hours to be added = 1 0 1 0 − 2 4 × 4 2 = 2
So, the required date and time is 1 2 : 3 0 A M o f 1 1 M a r c h , 2 0 1 2