find the time lapse

Question

A. 1:23 b. 4:16   find time lapse

Answer 1

Do you mean, what is the time difference between these the two times given? 

The easiest way for me to think about this is to first add whole hours and then work backwards: 

 

1:23 + 3 hours would be 4:23 elapsed time. But that overshoots our target time by the difference between 4:23 and 4:16. By how much would this estimate be wrong? We have 7 minutes too much, so that's what I'd subtract from my initial addition: 3:00 - :07 = 2:53

 

let's check: 

 

  1:23 

+2:53

  3:76

 

76 minutes is 60 + 16, so I can add a whole hour plus 16 minutes to the 3 hours, and I get 4:16. 

 

Let's look at this another way: 

  4:16 

- 1:23

 

since the 0:23 on the bottom is too large to subtract from the 0:16 on the top, let's borrow 0:60 from the 4 minutes on the top and make the minutes on the top 60 + 16 = 76

 

Then we have a new problem: 

 3:76

-1:23

 2:53

Answer 2

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