open number line. references teaching student-centered mathematics grades k-3, john a. van de walle,...
TRANSCRIPT
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.