Q.What time will it be after 1275 hours, if the present time is 9:00 p.m. ? (A) 11 p.m. (B) 12 p.m. (C) 9 p.m. (D) 9 a.m.

Elapsed Time: The Intuition

Imagine you're waiting for a friend. You check your watch at 2:15 PM. They finally arrive at 3:45 PM. How long did you wait? That's elapsed time — the amount of time that passes between a starting moment and an ending moment.

It's the simplest question in the world: "How much time went by?" But the trick is that time doesn't move in a straight, decimal line. An hour is 60 minutes, not 100. A day is 24 hours. So calculating elapsed time is really just subtracting times, but with a twist because of how we measure time.

The Precise Statement

That's it. The whole concept. But the devil is in the execution — because you can't just subtract 2:15 from 3:45 like you'd subtract 215 from 345.

How to Actually Do It

There are two reliable methods. Pick the one that clicks for you.

Method 1: The Number Line (Best for intuition)

Draw a mental timeline. Jump from the start time to the end time in convenient chunks.

Example: From 2:15 PM to 3:45 PM.

• From 2:15 to 3:00 is 45 minutes.
• From 3:00 to 3:45 is another 45 minutes.
• Total: 45 + 45 = 90 minutes = 1 hour 30 minutes.

This method works for any problem. Break the gap into easy pieces: first to the next hour, then to the target hour, then to the exact minute.

Method 2: Column Subtraction (Best for speed)

Write the times in hours and minutes, then subtract — but borrow 60 minutes from the hours column when needed, just like you'd borrow 10 in regular subtraction.

Example: From 2:15 to 3:45.

  Hours  Minutes
    3      45
  - 2      15
  ------------
    1      30

Answer: 1 hour 30 minutes.

Trickier example: From 9:50 AM to 11:10 AM.

  Hours  Minutes
   11      10
-   9      50

You can't subtract 50 from 10. So borrow 1 hour (60 minutes) from the 11:

  Hours  Minutes
   10      70   (11 becomes 10, 10 becomes 10+60=70)
-   9      50 …