Open Number Line

Strategies for Addition

Addition – Student 136 + 24

+10

36

+10 +4

36 + 24 = 60

46 56 60

Addition – Student 236 + 24

+4

36

+10 +10

36 + 24 = 60

40 50 60

Addition – Student 336 + 24

36

+20 +4

36 + 24 = 60

56 60

Strategies for Subtraction

Subtraction – Student 153 - 37

+10

37

+3 +3

53 - 37 = 16

47 50 53

Strategy: count up from

the smallest number

10 + 3 + 3 = 16

Subtraction – Student 253 - 37

-3

37

-3 -10

53 - 37 = 16

40 43 53

Strategy: count back

from the largest number

3 + 3 + 10 = 16

Subtraction – Student 353 - 37

-4

16

-3 -10

53 - 37 = 16

33 43 53

Strategy: c

ount back

from th

e largest number

-10-10

20 23

Using Benchmarks

How long is the movie?

I started watching a movie at 3:30 pm and it ended at 4:45 pm.

Elapsed TimeThe movie started at 3:30 and ended at 4:45.

How long was the movie?+30 min

3:30

30 + 30 + 15 = 75 minutes = 1 hour 15 minutes

4:00 4:30 4:45

+30 min +15 min

Strategy: S

tart at 3

:30

and add time increments

to th

e hour or ½

hour,

(benchmarks), then

continue until end tim

e.

How much time is there between school and bedtime?

How much time is there between the time school is out (3:40 pm) and bedtime (8:15 pm)?

Elapsed Time – using benchmarksHow much time is there between 3:40 and

8:15?

+20 min

3:40

4 hours + 20 min. + 15 min.= 4 hours 35 minutes

4:00 8:00 8:15

+4 hours +15 minStrategy: S

tart at 3

:40

and add time increments

to th

e ½ hour b

enchmarks,

then continue increments.

Time over the 12:00 hour

How much time is there between 10:30 am and 2:45 pm?

Elapsed Time – over 12 o’clock hourHow much time is there between 10:30 am

and 2:45 pm?

+30 min.

1 hr. + 2 hr. + 30 min. + 45 min. = 3 hr. 75 min. = 4 hr. 15 min.

12:00noon

2:00 2:45

+2 hours +45 min

11:0010:30

+1 hour

Strategy: A

dd increments

to 12:00, th

en continue

benchmark increments.

Find the ending time

What time is 4 hours and 30 minutes from 6:55?

Finding the ending time – Student 1What time is it 4 hours and 30 minutes

from 6:55?

The time is 11:25, which is 4 hrs. and 30 min. after 6:55.

11:00 11:25

+25 min

7:006:55

+4 hr.+5 minStra

tegy: Add m

inute

increments to th

e ½ hour

benchmark, then hours, th

en

minutes.

Finding the ending time – Student 2What time is it 4 hours and 30 minutes

from 6:55?

The time is 11:25, which is 4 hrs. and 30 min. after 6:55.

11:0011:25

+25min

7:556:55

+1 hr.+1 hr.+1 hr.+1 hr. +5 min

9:558:55 10:55

Strategy: A

dd hour increments

until close, th

en minutes to

the

½ hour, then m

inutes.

Find the start time

What time did we start on our trip if we arrived at 8:17 and it took 3 hours and 10 minutes?

Finding the start timeWhat time did we start on our trip if we

arrived at 8:17 and it took 3 hours and 10 minutes? -10 min. -3 hr.

The start time is 5:07.

5:07 5:17 8:17

Strategy: S

ubtract th

e hours

then minutes.

Find the start time

What time do I need to wake up if I have to be at school at 8:15 am and it takes me 1 hour and 45 minutes to get ready?

Finding the start timeWhat time do I need to wake up if I have to

be at school at 8:15 am and it takes me 1 hour and 45 minutes to get ready?

-15 min. -1 hr.

I have to wake up at 6:30 AM.

6:45 7:15 8:156:30 7:00

-15 min.-15 min.

Strategy: S

ubtract th

e hour,

then m

inute benchmarks.