LemonmathSelf-study sheet

Grade 2 · Lesson 2.1

Addition bridging through 10 (within 20)

Name: Date: Time spent: min

Goals

Add two numbers whose total is more than 10, for example $8+5$ .
Use the "make 10" trick to add quickly, without counting one by one.
Solve a word problem with one addition.

Remember

To add across $10$ , make 10: split the second number into the part that makes $10$ and the part that is left.
Example: $8+5=8+2+3=10+3=13$ .
Swapping the addends does not change the sum; add on to the bigger number to make it easier.
Questions with "altogether" or "both" usually need addition; remember the unit in the answer.

Exercises

Exercise 1

Work out $9+3$ .

Exercise 2

Work out $8+4$ .

Exercise 3

Work out $7+5$ .

Exercise 4

Work out $5+9$ .

Exercise 5

Write $>$ , $<$ or $=$ in the box: $8+6 \;\square\; 15$ .

Exercise 6

In a garden there are $9$ hens and $6$ cockerels. How many chickens are there altogether?

Exercise 7

Remember the last lesson: what number comes just after $12$ ? Then work out (the number just after $12$ ) $+\,7$ .

Exercise 8 Challenge

Find the missing number: $\square+8=15$ .

Mini test

15 minutes, without looking back at the lesson. Part I: circle one letter; Part II: write T or F for each statement; Part III: write the answer in the box.

Part I. Multiple choice

Question 1.

9+5

equals

13

.B.

14

.C.

15

.D.

10

Question 2. To work out

8+7

with the make-10 trick, you split

7

into

1

and

6

.B.

3

and

4

.C.

2

and

5

.D.

2

and

4

Question 3. Which sum equals

13

6+7

.B.

6+8

.C.

5+7

.D.

9+5

Question 4. Mai has

8

flowers and Ha has

6

flowers. How many flowers do the two girls have altogether?

2

flowers.B.

13

flowers.C.

14

flowers.D.

15

flowers.

Part II. True or false

Question 1. Look at the sum

7+8

a) It can be written as $8+7$ without changing the answer.	T / F
b) $7+8=7+3+5$ .	T / F
c) $7+8=14$ .	T / F
d) $7+8$ is greater than $14$ .	T / F

Part III. Short answer

Question 1. Work out

9+9

Question 2. There are

7

birds on a branch and

4

more fly in. How many birds are on the branch altogether?

Score: ........ / 10

Hints (only when stuck)

Exercise 1.

What you need: make $10$ : $9$ needs $1$ more.

Steps:

Split $3$ into $1$ and $2$ .
Work out $9+1$ , then add $2$ .

Exercise 2.

What you need: $8$ needs $2$ more to make $10$ .

Steps:

Split $4$ into $2$ and $2$ .
Work out $8+2$ , then add what is left.

Exercise 3.

What you need: $7$ needs $3$ more to make $10$ .

Steps:

Split $5$ into $3$ and $2$ .
Work out $7+3$ , then add $2$ .

Exercise 4.

What you need: swapping the two addends does not change the sum.

Steps:

Write $5+9$ as $9+5$ .
$9$ needs $1$ more: split $5$ into $1$ and $4$ .

Exercise 5.

What you need: work out the sum first, then compare the two numbers.

Steps:

Work out $8+6$ with the make-10 trick.
Compare the result with $15$ .

Exercise 6.

What you need: "altogether" means putting together: use addition.

Steps:

What do we know? $9$ hens and $6$ cockerels. What is asked? How many chickens altogether.
Work out $9+6$ and write the answer with its unit.

Exercise 7.

What you need: the number just after a number is $1$ more than it.

Steps:

Find the number just after $12$ .
Add $7$ to it (count on, or add the ones).

Exercise 8.

What you need: $8$ needs $2$ more to make $10$ ; then how many more to reach $15$ ?

Steps:

From $8$ to $10$ you need $2$ .
From $10$ to $15$ you need $5$ .
Add the two parts: $2+5$ .

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