Cogito
Grade 3 Math · Chapter 2 · Lesson 7
Time Intervals
How long did that take?
10 problems · about 14 minutes · 3.MD.A.1
What this lesson teaches
The child measures and calculates time intervals in minutes, including across an hour.
- An interval is how long something lasts.
- Count on to the next hour, then count the rest.
- Add the two jumps to get the total.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Telling Time to the Minute: One mark past the 9. How many minutes past the hour?
Answer 46
Why 45 and 1 more is 46.
Review — Subtracting Within 1,000 Fluently: 905 − 348 = ?
Answer 557
Why 905 − 348 = 557.
Review — Adding Within 1,000 Fluently: 385 + 247 = ?
Answer 632
Why 385 + 247 = 632.
Warm Up
Straightforward practice. Get the method working first.
3 problemsFrom 7:45 to 8:10. How many minutes?
Answer 25
Why 15 + 10 = 25 minutes.
Why count on to the hour first?
Answer Because an hour is 60 minutes, not 100.
Why The hour boundary is where straightforward subtraction breaks down.
From 1:10 to 1:45. How many minutes?
Answer 35
Why Same hour.
Build It Up
The same ideas with more to keep track of.
1 problemFrom 5:50 to 6:20. How many minutes?
Answer 30
Why 10 to the hour, then 20.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problemsFrom 9:35 to 10:05. How many minutes?
Answer 30
Why 25 to the hour, then 5.
Break Time: Break starts at 10:45 and ends at 11:05. How long is it?
Answer 20 minutes
Why 15 + 5 = 20 minutes.
The Lesson: A lesson runs from 2:20 to 2:55. How many minutes is that?
Answer 35 minutes
Why 55 − 20 = 35 minutes.