Solving exercises on page 75 of Math Workbook Grade 4

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Guidance on solving exercises on page 75 of Math Workbook Grade 4 includes solving methods

1. Exercise 1 on page 75 of Math Workbook Grade 4

Problem:
Write the appropriate number in the blank:
a) 10 kg = ... sparrows
100kg = ... catties
50 kg = ... sparrows
300kg = ... catties
80kg = ... sparrows
1200kg = ... catties
b) 1000kg = ... tons
10 catties = ... tons
8000kg = ... tons
30 catties = ... tons
15 000kg = ... tons
200 catties = ... tons
c) 100cm² = ... dm²
100dm² = ... m²
800cm² = ... dm²
900dm² = ... m²
1700cm² = ... dm²
1000dm² = ... m²

Solution:
- According to the unit conversion table of length/mass:
+ Each larger unit is 10 times the adjacent smaller unit
+ Each smaller unit is 1/10 of the adjacent larger unit
=> The sequence of units:
- Mass: Ton; catty; sparrow; kilogram (kg); hectogram (hg); decagram (dag); gram (g)
- Length: kilometer (km); hectometer (hm); decameter (dam); meter (m); decimeter (dm); centimeter (cm); millimeter (mm)
- According to the unit conversion table of area:
+ Each unit of area is 100 times the adjacent smaller unit
+ Each smaller unit of area is 1/100 of the adjacent larger unit.

Answer:
a) 10kg = 1 sparrow
100kg = 1 catty
50kg = 5 sparrows
300kg = 3 catties
80kg = 8 sparrows
1200kg = 12 catties
b) 1000kg = 1 ton
10 catties = 1 ton
8000kg = 8 tons
30 catties = 3 tons
15 000kg = 15 tons
200 catties = 20 tons
c) 100cm² = 1dm²
100dm² = 1m²
800cm² = 8dm²
900dm² = 9m²
1700cm² = 17dm²
1000dm² = 10m²

2. Exercise 2 on page 75 of Math Workbook Grade 4

Problem:
Calculate:
a) 268 x 235                        b) 475 x 205                          c) 45 x 12 + 8
324 x 250                                309 x 207                               45 x (12 + 8)

Solution:
- For multiplication operations: Set up the multiplication as previously instructed in the previous exercises.
- For expressions containing parentheses: Perform the operation inside the parentheses first, then outside the parentheses.
- For expressions containing both multiplication and addition: Perform multiplication first, then addition. 

Answer:
a) 268 x 235 = 62980
     324 x 250 = 8100
b) 475 x 205 = 97375
    309 x 207 = 63963
c) 45 x 12 + 8 = 540 + 8 = 548
    45 x (12 + 8) = 45 x 20 = 900

3. Exercise 3 on page 75 of Math Workbook Grade 4

Problem:
Calculate the most convenient way:
a) 2 x 39 x 5;                          b) 302 x 16 + 302 x 4;                        c) 769 x 85 - 769 x 75.

Solution:
- For question a): Apply the associative property of multiplication: a x b x c = a x (b x c), group the numbers whose product is a round number, then multiply by the remaining number
- For question b): Apply the calculation method: a x b + a x c = a x (b + c)
- For question c): Apply the calculation method: a x b - a x c = a x (b - c)

Answer:
a) 2 x 39 x 5                                  b) 302 x 16 + 302 x 4                                  c) 769 x 85 - 769 x 75
= 39 x (2 x 5)                                      = 302 x (16 + 4)                                            = 769 x (85 - 75)
= 39 x 10 = 390                                                                 = 302 x 20 = 6040                                        = 769 x 10 = 7690

4. Solving Exercise 4 on page 75 of Math Workbook Grade 4

Problem:
Two water pipes start flowing into a tank. The first pipe flows at a rate of 25 liters per minute. The second pipe flows at a rate of 15 liters per minute. How many liters of water will flow into the tank after 1 hour and 15 minutes?

Solution:
* Solution 1:
- Convert the time unit to minutes
- Calculate the number of liters of water flowing into the tank per minute by adding the flow rates of the two pipes
- To find out how many liters of water will flow into the tank after 1 hour and 15 minutes, multiply the time the two pipes flow into the tank by the number of liters of water both pipes can flow into the tank per minute. 

* Solution 2:
- Convert the time unit to minutes 
- Calculate the number of liters of water the first pipe can flow into the tank after 1 hour and 15 minutes by multiplying the time by the flow rate per minute
- Calculate the number of liters of water the second pipe can flow into the tank after 1 hour and 15 minutes by multiplying the time by the flow rate per minute
- Calculate the total number of liters of water both pipes can flow into the tank after 1 hour and 15 minutes by adding the two results obtained above. 

Answer:
Solution 1:
We have 1 hour and 15 minutes = 75 minutes.
Every minute, the two water pipes flowing into the tank together are:
25 + 15 = 40 (liters)
After 1 hour and 15 minutes, both pipes can flow into the tank:
40 x 75 = 3000 (liters)
Answer: 3000 liters of water.

Solution 2:
1 hour and 15 minutes = 75 minutes
After 1 hour and 15 minutes, the first pipe can flow into the tank:
25 x 75 = 1875 (liters)
After 1 hour and 15 minutes, the second pipe can flow into the tank:
15 x 75 = 1125 (liters)
After 1 hour and 15 minutes, both pipes can flow into the tank:
1875 + 1125 = 3000 (liters)
Answer: 3000 liters of water.

Solving Exercise 5 on page 75 of Mathematics 4 textbook:

Method:
- Formula to find the area of a square: S = a x a or S = a^2
Where: S denotes the area of the square; a represents the length of the side
- Applying the above formula, substitute the given values into the formula, calculate carefully to find the most accurate result; note to add the area symbol m^2 after the result.

Answer:
a) To find the area of a square, multiply the length of one side by itself:
S = a x a
b) For a = 25m, then S = 25 x 25 = 625 (m^2)

Here's the solution for exercise 75 in Math book for 4th grade. Students can review the solutions from exercise 74 or get a sneak peek into exercise 76 to excel in Math.

Solving problems 1 to 5 on page 75 of Math textbook for 4th graders.

- Solution for problem 1 on page 75 of Math textbook for 4th graders.

- Solution for problem 2 on page 75 of Math textbook for 4th graders.

- Solution for problem 3 on page 75 of Math textbook for 4th graders.

- Solution for problem 4 on page 75 of Math textbook for 4th graders.

- Solution for problem 5 on page 75 of Math textbook for 4th graders.

With the solution to exercise 75 in the Math book for 4th graders, students have gained additional skills in solving Math problems. Additionally, they need to revise Natural Numbers and prepare for the next topic, Charts, in Chapter I with exercises 30, 31, 32 for better understanding of this lesson.

Please pay attention to the hints for solving Math problems on page 26 as this is one of the important lessons related to everyday life as well as to grasp the knowledge and study Math 4 well.