We want to determine four plus three
using a number line, or determine
the sum of four and three.
For review remember, four
and three are called addends,
and the result of the
addition is called the sum.
To model the sum we first
model four on the number line
by starting at zero, and
moving right four units.
Starting at zero we have
one, two, three four.
Then because we have plus three,
from four we move right three more units.
So four plus one, plus two, plus three.
And we can see the sum is seven.
Four plus three equals seven.
We could also think of this as four
increased by three is seven.
Let's look at two more examples.
Here we have nine plus seven.
We first model nine on the number line
by starting at zero, and
moving right nine units.
We need to be careful here because notice
how there are labels very two units,
but there is a tick mark every one unit.
So starting at zero we
have one, two, three,
four, five, six, seven, eight, nine.
Let's go ahead and make a point here,
and let's label this nine.
And then because we have
plus seven from nine,
we move seven more units to the right.
We have plus one, plus two, plus three,
plus four, plus five,
plus six, and plus seven.
Now we know nine plus seven equals 16.
Where again nine and seven are
the addends, 16 is the sum.
And then finally we have 12 plus 19.
So to model 12 we could start
at zero and then jump to 12.
Let's keep it consistent
and just count by ones.
And again notice how we have
labels every five units,
and tick marks every one unit.
So starting at zero we have
one, two, three, four, five,
six, seven, eight, nine, 10, 11, 12.
Let's go ahead and make a
point here and label this 12.
And then because we have plus 19,
from here we move 19
more units to the right.
So plus one, two, three, four, five, six,
seven, eight, nine, 10, 11, 12,
13, 14, 15, 16,
17, 18, 19.
Notice how this is 31 on the
number line, which is the sum.
12 plus 19 equals 31.
I hope you found this helpful.
