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Solving Math problems for 3rd graders on pages 80 and 81 of the book 'Horizon of Creativity' Volume 2
Solving exercises on pages 80 and 81 of Math 3 Workbook Volume 2, from the book 'Horizon of Creativity':
Reviewing Arithmetic Operations
1. Solve Exercise 1 Page 80 Math Grade 3
Problem: Set up the calculation and solve.
Solution Guide:
For addition and subtraction: Set up the calculation vertically, align numbers in the same column. Add/subtract numbers from right to left.
For multiplication: Set up the calculation and multiply sequentially from right to left.
Answer:
2. Solve Exercise 2 Page 80 Math Grade 3
Problem: Mental calculation.
Solution Guide: Mentally calculate the results of multiplication, division, addition, and subtraction with round thousands and tens of thousands.
Note:
+ For expressions containing only addition, subtraction, multiplication, or division, perform them from left to right.
+ For expressions with parentheses, perform operations inside the parentheses first.
Answer:
a) 2 x (3,000 + 2,000) = 2 x 5,000
= 10,000
b) 12,000 : 3 : 4 = 4,000 : 4
= 1,000
c) 19,000 - 3,000 x 3 = 19,000 - 9,000
= 10,000
d) (10,000 - 10,000) : 8 = 0 : 8
= 0
3. Solve Exercise 3 Page 80 Math Grade 3
Problem: Which number does each figure conceal?
Solution Guide:
+ Identify the roles of the concealed numbers in the arithmetic operation.
+ Find the concealed numbers.
Answer:
a) We have: 2,000 - 1,200 = 800.
So, the square conceals the number 800.
b) We have: 1,800 + 1,700 = 3,500.
So, the triangle conceals the number 3,500.
c) We have: 2,000 : 5 = 400.
So, the quadrilateral conceals the number 400.
d) We have: 800 x 3 = 2,400.
So, the circle conceals the number 2,400.
- See also: Solving exercises on pages 82, 83, 84 Math 3 Workbook Volume 2, from the book 'Horizon of Creativity'
4. Solve Exercise 4 Page 80 Math Grade 3
Problem: Choose the appropriate number for each question.
Solution Guide:
+ To multiply a number by a certain factor, multiply the number by that factor.
+ To divide a number by a certain factor, divide the number by that factor.
+ To add a unit to a given number, add the unit to that number.
+ To subtract a unit from a given number, subtract the unit from that number.
Answer:
5. Solve Exercise 5 Page 80 Math Grade 3
Problem: Choose the correct answer.
Solution Guide:
a) b) Calculate and choose the appropriate answer.
c) To calculate the number of third-grade students in that school, multiply the number of students in one class by 7 and then subtract 1.
Answer:
6. Solve Exercise 6 Page 81 Math Grade 3
Problem: Anh Hai plans to run 2 km every day. Today, he runs 6 laps around a rectangular sports field with a length of 115 m and a width of 75 m. Did Anh Hai achieve his daily goal?
Solution Guide:
Step 1: Calculate the distance Anh Hai runs in 1 lap (equal to the perimeter of the rectangle).
Step 2: Calculate the distance Anh Hai runs in 6 laps.
Step 3: Compare the distance Anh Hai runs with the set goal and draw a conclusion.
Answer:
When Anh Hai runs 1 lap around the rectangular sports field, the distance he runs equals the perimeter of the field.
The distance he runs in each lap is:
(115 + 75) x 2 = 380 (m)
Today, Anh Hai runs a total distance of:
380 x 6 = 2,280 (m)
Convert 2 km to 2,000 m. We have: 2,280 m > 2,000 m.
Therefore, today Anh Hai has achieved his daily goal.
7. Solve Exercise 7 Page 81 Math Grade 3
Problem: Solve the problem summarized below:
Solution Guide:
Step 1: Calculate the weight of the cow = weight of the pig x 3.
Step 2: Calculate the total weight of the cow and pig = weight of the pig + weight of the cow.
Answer:
+ The problem can be stated as follows:
The pig weighs 160 kg. The cow weighs 3 times the pig. How much do both the cow and the pig weigh altogether?
+ Solution:
The weight of the cow in kilograms is:
160 x 3 = 480 (kg)
The total weight of both the cow and the pig in kilograms is:
160 + 480 = 640 (kg)
Answer: 640 kg.
8. Solve Exercise 8 Page 81 Math Grade 3
Problem: a) Using the digits 3, 4, 1, 7, 5, write:
The largest 5-digit number.
The smallest 5-digit number.
b) Calculate the sum of the two numbers you just wrote.
Solution Guide:
To write the largest 5-digit number, select digits for the ten thousands, thousands, hundreds, tens, and units places in descending order.
To write the smallest 5-digit number, select digits for the ten thousands, thousands, hundreds, tens, and units places in ascending order.
Answer:
a) The largest 5-digit number using the digits 3, 4, 1, 7, 5 is: 75,431.
The smallest 5-digit number using the digits 3, 4, 1, 7, 5 is: 13,457.
c) The sum of the two numbers just written is: 75,431 + 13,457 = 88,888.
9. Solve Exercise 9 Page 81 Math Grade 3
Problem: Digit ?.
Solution Guide: Follow the rule of setting up the calculation and solve to determine the appropriate digit for the '?'.
Answer:
Exploration
Problem: Digit ?
There is a species of marsupial mouse that weighs only 1 g at birth but grows to 90 kg as an adult. The adult marsupial mouse weighs ? times its weight at birth.
Solution Guide: To calculate how many times the adult marsupial mouse weighs compared to its weight at birth, divide the weight as an adult by the weight at birth (using the same unit of measurement).
Answer:
Convert: 90 kg = 90,000 g.
The adult marsupial mouse weighs ? times its weight at birth:
90,000 : 1 = 90,000 (times).
So, fill in the number 90,000.
Solving exercises on pages 80 and 81 of Math Grade 3 Workbook, Chân Trời Sáng Tạo series, provides detailed solutions. Pay attention to the instructions combined with the learned knowledge for better understanding and easier completion.
