Problem solved with two operations

### 1.1. Problem solved with two operations

__ Problem 1:__ The top row has 3 trumpets, the bottom row has more than 2 trumpets. Ask :

a) How many trumpets are there in the bottom row?

b) How many trumpets are there in both rows?

*Summary:*

**Solution guide:**

a) The number of trumpets in the bottom row is:

3 + 2 = 5 (piece)

b) The number of trumpets in both rows is :

3 + 5 = 8 (piece)

Answer: a) 5 trumpets

b) 8 trumpets

** Problem 2:** The first tank has 4 fish, the second tank has 3 more fish than the first tank. How many fish are there in both tanks?

*Summary:*

**Solution guide:**

Number of fish in the second tank is:

4 + 3 = 7 (child)

Number of fish in both tanks is :

4 + 7 = 11 (child)

Answer: 11 fish

### 1.2. Problem solved with two operations (continued)

__ Problem :__ A shop sells 6 bicycles on Saturday, and on Sunday sells twice as many bicycles as above. How many bicycles did the store sell on both days?

*Summary:*

*Solution guide:*

The number of bicycles sold on Sunday is:

6 x 2 = 12 (vehicle)

The number of bicycles sold in both days is :

6 + 12 = 18 (vehicle)

Answer: 18 bicycles

### 1.3. Textbook exercise solution page 50

**Lesson 1: **I have 15 postcards, you have 7 less than me. How many postcards do both brothers have?

*Solution guide:*

*Summary:*

*Solution:*

My postcard number is:

15 – 7 = 8 (plates)

The number of postcards of the two brothers is:

15 + 8 = 23 (plate)

Answer: 23 sheets.

**Lesson 2: **The first barrel holds 18 liters of oil, the second contains 6 liters more oil than the first one. How many liters of oil are in both tanks?

**Solution guide:**

*Summary:*

- Find the number of liters of oil in barrel 2 by adding the number of liters of oil in barrel 1 plus 6.
- Find the number of liters of oil in both tanks by adding 18ℓ18ℓ plus the number you just found.

*Solution:*

The number of liters of oil in the second barrel is:

18 + 6 = 24 (liters)

The number of liters of oil in both tanks is:

18 + 24 = 42 (liters)

Answer: 42 liters.

**Lesson 3:** State the problem according to the following summary and then solve it.

*Solution guide:*

- From the summary, determine the quantities and their values, information about more, less, and the requirements of the problem.
- Find ways to solve and present the problem:

+ Find the value of the unknown quantity: Take the kilogram of the bag of rice plus 5kg.

+ Find the weights of both bags by adding 27kg plus the number you just found.

*Solution:*

The problem can be stated as follows:

The bag of rice weighs 27 kg, the bag of corn weighs 5 kg more than the bag of rice. How many kilograms did both bags weigh?

*Solution:*

A bag of corn weighing kilograms is:

27 + 5 = 32 (kg)

Both bags weigh in kilograms:

27 + 32 = 59 (kg)

Answer: 59 kg.

### 1.4. Textbook exercise solution page 51

**Lesson 1:** The distance from the house to the district market is 5km long, the distance from the district market to the provincial post office is three times longer than the distance from the house to the district market (according to the following diagram). How many kilometers is the distance from home to the provincial post office?

*Solution guide:*

- Find the distance from the district market to the provincial post office.
- Calculate the total distance from the house to the district market and from the district market to the provincial post office.

*Solution: *

The distance from the district market to the provincial post office in kilometers is :

5 x 3 = 15 (km)

The distance from home to the provincial post office in kilometers is:

5 + 15 = 20 (km)

Answer: 20km.

**Lesson 2:** A bucket contains 24 liters of honey, take out \(\frac{1}{3}\) that number of liters of honey. How many liters of honey are left in the barrel?

__Solution guide:__

*Summary:*

Yes : 24ℓ honey

Take out : \(\frac{1}{3}\) the number of liters of honey

Remaining : … ℓ honey ?

– Find the number of liters of honey taken out by dividing the original number of liters of honey by 3.

– Take the original number of liters of honey minus the number of liters of honey taken out.

*Solution: *

The number of liters of honey taken out is:

24 : 3 = 8 (ℓ)

In the remaining barrel, the number of liters of honey is:

24 – 8 = 16 (ℓ)

Answer: 16ℓ.

**Lesson 3:** Number?

*Solution guide:*

- To multiply a number many times, we multiply that number by the number of times.
- To reduce a number many times we divide that number by the number of times.
- To add (subtract) a number of units, we add (subtract) the number of units.
- Perform the appropriate calculations from left to right and then fill in the blanks with the results.

*Solution:*

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