Grade 1 Math Adding Doubles
Adding Doubles
What is adding
doubles?
When two addends are same, then the adding process is called adding doubles.
Example:
1 + 1 = 2.
Here, two addends
are 1 and 1. They are same.
Adding Doubles
Table:
Adding doubles with
Zero:
When two addends
are 0, then the sum is 0 also.
0 + 0 = 0.
Adding doubles by
multiplication:
First look at the
following table:
|
Adding Doubles
|
Multiplying by 2
|
|
0 +
0 = 0.
|
0 ×
2 = 0.
|
|
1 +
1 = 2.
|
1 ×
2 = 2.
|
|
2 +
2 = 4.
|
2 ×
2 = 4.
|
|
5 +
5 = 10.
|
5 ×
2 = 10.
|
|
10
+ 10 = 20.
|
10 ×
2 = 10.
|
So, the tables rule follow: a + a = 2 × a
or, adding doubles
= 2 × addend.
Using double fact
for addition:
when two addends are
added, then break down the big addend with two numbers where one number will be
the same as the small addend. As of now, there have two same numbers, so we can use
adding doubles rules.
Example:
8 + 7 = ?
Here,
8 + 7
= (1 + 7) + 7 [break
down of 8 = 1 + 7]
= 1 + 7 + 7
= 1 + (7 + 7) [use
adding double 7 + 7 = 14]
= 1 + 14
= 15
So, 8 + 7 = 15.
1. Find the sun of 3 and double of 3.
Answer:
double of 3 = 3 × 2
= 6.
So, 3 + 6 = 9.
That means, the sum
of 3 and doubles = 3 + 3 × 2 = 3 + 6 = 9.
2. Find the correct answer?
3 + double of 4 = ?
(a) 10
(b) 11
(c) 12
(d) 8
Answer: b
[3 + double of 4 =
3 + 4 × 2 = 3 + 8 = 11]
3. Use the doubles fact for addition.
(a) 9 + 8
(b) 10 + 9
(c) 12 + 9
(d) 6 + 7
Solution:
(a)
9 + 8
= 1 + 8 + 8 [break
down, 1+8 = 9]
= 1 + 16 [adding doubles, 8+8 = 16]
= 17
(b)
10 + 9
= 1 + 9 + 9 [break down,10 = 1 + 9]
= 1 + 18. [double
fact, 9 + 9 =18]
= 19
(c)
12 + 9
= 3 + 9 + 9 [break down, 12 = 3 + 9]
= 3 + 18 [adding doubles, 9 + 9 =18]
= 21
(d)
6 + 7
= 6 + 6 + 1 [break down, 7 = 6 + 1]
= 12 + 1 [adding
doubles, 6 + 6 = 12]
= 13
4. Fill in the blanks.
(a) 8 + 8 = _____.
(b) 8 + 9 = _____.
(c) 5 + 4 = _____.
Answer:
(a) 8 + 8 = 16 [using
double fact]
(b) 8 + 9 = 47 [using
double fact]
(c) 5 + 4 = 9 [using
double fact]