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Solving Grade 5 Math Problems - Pages 39, 40, 41 VBT Volume 2, Focused Practice, Exercise 117 provides detailed solutions and answers for exercises 1, 2, 3, 4. Students can refer to reinforce knowledge and practice volume and percentage calculations effectively.
Grade 5 Math Exercises - Pages 39, 40, 41 VBT Volume 2, Focused Practice, Exercise 117
1. Solve problem 1 - Math exercise book for 5th grade, exercise 1 on page 39
Problem Statement:
Dung mentally calculates 15% of 120 as follows:
10% of 120 is 12
5% of 120 is 6
So, 15% of 120 equals 18.
a. Dung, please fill in the blanks with the correct numbers to find 35% of 80:
............% of 80 equals ............
............% of 80 equals ............
............% of 80 equals ............
............% of 80 equals ............
............% of 80 equals ............
b. Describe a similar method to find 22.5% of 240:
............% of 240 equals ............
............% of 240 equals ............
............% of 240 equals ............
............% of 240 equals ............
............% of 240 equals ............
Solution Method
*) - Break down 15% = 10% + 5%
- Mentally calculate 10% of 80 by dividing 80 by 10.
Calculate 5% by finding 10% of 80 and dividing by 2.
Similarly, find 35% of 80 and 22.5% of 240 using the same method.
Answer
a. According to your method, Dung, write the appropriate number in the blank to find 35% of 80:
10% of 80 equals 8
20% of 80 equals 16
30% of 80 equals 24
5% of 80 equals 4
35% of 80 equals 28
b. Describe the same method used above to find 22.5% of 240:
10% of 240 equals 24
20% of 240 equals 48
2% of 240 equals 4.8
0.5% of 240 equals 1.2
22.5% of 240 equals 54
2. Solve problem 2 - Math exercise book for 5th grade, exercise 2 on page 39
Problem:
The volume of the small cube is 125cm3 and is 5/8 of the volume of the large cube. Ask:
a) What percentage of the volume of the small cube is the volume of the large cube?
b) What is the volume of the large cube in cubic meters?
Solution Method
- Find the ratio of the volume of the large cube to the volume of the small cube and express it as a percentage.
- To find the volume of the large cube, multiply the volume of the small cube by the ratio of the volume of the large cube to the volume of the small cube.
Answer
a) The volume of the small cube is 5/8 of the volume of the large cube, so the ratio of the volume of the large cube to the volume of the small cube is 8/5
Percentage ratio of the volume of the large cube to the volume of the small cube:
8/5 x 100 = 160%
b) Volume of the large cube:
125 ⨯ 8/5 = 200 (cm3)
Answer: a. 160% ; b. 200cm3
3. Solve problem 3 - Math exercise book for 5th grade, exercise 2 on page 40
Problem:
Hoa arranges small cubes with a side length of 1cm into the shape below. Ask:
a. How many small cubes are there in the shape below?
b. If the outer surfaces of the shape below are painted, how many square centimeters of paint are needed?
Solution Method
- Observe the diagram to find the number of small cubes in the given shape.
- Apply the formula for calculating the area of one face: Area of one face = side ⨯ side.
Answer
a. Looking at the shape, we see there are 20 small cubes.
b. To paint the outer surfaces of the above shape, we need to paint 12 large faces and 4 small faces.
The area of 12 large faces is:
2 ⨯ 2 ⨯ 12 = 48 (cm2)
The area of the 4 small faces is also the area of 2 large faces:
2 ⨯ 4 = 8 (cm2)
The area to be painted is:
48 + 8 = 56 (cm2)
4. Solve problem 4 - Math exercise book for 5th grade, exercise 2 on page 41
Problem:
Circle the letter before the correct answer:
Knowing that 1 cell has a volume of 1cm3. The volume of the shape below is:
A. 27cm3
B. 21cm3
C. 18cm3
D. 15cm3
Solution Method
- Observe the diagram to find the number of small cubes in the given shape.
- The volume of the shape = volume of 1 small cube ⨯ number of small cubes in the shape.
Answer
The shape is made up of cubes:
3 ⨯ 3 ⨯ 2 = 18 cubes
The volume of the shape is:
18 ⨯ 1 = 18cm3
So choose answer C.
You are currently viewing the Math solving guide for Grade 5 pages 39, 40, 41 in Exercise Book 2. You can review the instructions for Grade 5 pages 37, 38 in Exercise Book 2 or preview the instructions for Grade 5 pages 41, 42 in Exercise Book 2 Introduction to cylinders. Introduction to spheres for a better understanding of the lesson.
Wishing you all success in learning math!
