Addition within 100 (addition without memory)
1.1. Knowledge to remember
– Know how to set, calculate and add two-digit numbers.
– Mental addition of numbers within 100 (addition do not remember);
– Apply to solve word problems.
– The first step to know about the property of addition: When swapping two numbers in an addition, the result does not change.
1.2. Math forms on Addition within 100 (addition without memory)
Form 1: Performing the calculation
Perform addition of two-digit numbers by adding from right to left the numbers in the units row and then adding the numbers in the tens place.
Form 2: Math problems with words
– Read and analyze the problem: Determine the given numbers, the number of increases or decreases and the requirements of the problem.
– Find the solution to the problem:
I rely on the keywords “add”, “less”, “all”, “remaining”… to determine the calculation needed for the problem.
Problems that require finding “both” or “all” often use addition to find the solution.
– Present the solution to the problem: Write clearly the solution, calculation, answer.
– Check the solution and the results you just found.
Form 3: Compare
To compare the value of two or more additions of two-digit numbers, perform the calculation and then compare the results.
1.3. Solve textbook exercises pages 154, 155
Lesson 1 page 154
Add the numbers from right to left.
Lesson 2 page 155
Calculate then calculate
35 + 12 60 + 38 6 + 43
41 + 34 22 + 40 54 + 2
– Set calculation: Write the digits in the same row and one column.
– Calculation: Add the numbers from right to left in turn.
Lesson 3 page 155
Class 1A planted 35 trees, class 2A planted 50 trees. How many trees can the two classes plant in all?
Class 1A: 35 trees
Class 2A: 50 trees
Both: … tree?
To find the solution, we take the number of crops grown by class 1A plus the number of plants grown by class 2A.
The number of trees planted by both classes is:
35 + 50 = 85 (tree)
Answer: 85 trees
Lesson 4 page 155
Measure the length of each line segment and then write the measure:
– Use a ruler with centimeter divisions.
– Set the 0cm line to coincide with a line segment point; keep the edge of the ruler coincident with the line segment; If the remaining points coincide with the line, that is the length of the line segment.
Line segment AB is 9cm long.
The line segment CD is 13cm long.
Line segment MN is 12cm long.
1.4. Solving Textbook Exercises page 156
Lesson 1 page 156
Calculate then calculate:
47 + 22 40 + 20 12 + 4
51 + 35 80 + 9 8 + 31
– Set calculation: Write the digits in the same row and column together.
– Calculation: Add in turn from right to left.
Lesson 2 page 156
30 + 6 = 60 + 9 = 52 + 6 = 82 + 3 =
40 + 5 = 70 + 2 = 6 + 52= 3 + 82 =
Mentally calculate the numbers and fill in the blanks with the results.
30 + 6 = 36 60 + 9 = 69 52 + 6 = 58 82 + 3 = 85
40 + 5 = 45 70 + 2 = 72 6 + 52= 58 3 + 82 = 85
Lesson 3 page 156
My class has 21 girls and 14 boys. How many friends are there in your class?
Girlfriend: 21 friends
Boyfriend: 14 friends
All: … you ?
To find the solution, add the number of girlfriends plus the number of boyfriends.
In my class, all friends are:
21 + 14 = 35 (you)
Answer: 35 friends.
Lesson 4 page 156
Draw a line segment of length 8cm.
– Use a ruler with centimeter markings and a pencil.
– Mark a point, place the 0cm line of the ruler to coincide with that point, keep the ruler straight, mark the point lying on the 8cm line.
– Connect two points with a straightedge, we get a line segment 8cm long.
1.5. Textbook Exercises Page 157
Lesson 1 page 157
Add the numbers from right to left.
Lesson 2 page 157
20cm + 10cm = 30cm + 40cm =
14cm + 5cm = 25cm + 4cm =
32cm + 12cm = 43cm + 15cm =
Add the numbers and then write the units after the result you just found.
20cm + 10cm = 30cm 30cm + 40cm = 70cm
14cm + 5cm = 19cm 25cm + 4cm = 29cm
32cm + 12cm = 44cm 43cm + 15cm = 58cm
Lesson 3 page 157
Join (according to the pattern)
– Add numbers in the given calculations.
– Match with the appropriate result.
Do the calculations:
32 + 17 = 49
47 + 21 = 68
26 + 13 = 39
16 + 23 = 39
37 + 12 = 49
27 + 41 = 68
Joining the results we get:
Lesson 4 page 157
At first the snail crawled 15cm, then it crawled 14cm. How much gasoline can the snail crawl in all?
At the beginning: 15 cm
Later: 14 cm
All: … cm?
To find the answer, we add the crawl distance in two times.
The snail that crawls all the centimeters is:
15 + 14 = 29 (cm)