# Bài 41,42,43 ,44,45,46 ,47,48,49 ,50,51,52 ,53 trang 58,59,60 Toán

## A Step-by-Step Guide to Solving Equations

In this article, we will explore how to solve math problems using algebraic equations. We will focus on solving problems by setting up and solving equations, specifically in the field of algebra.

### Basic Knowledge

Here are the steps you should follow to solve problems using algebraic equations:

- Set up the equation by choosing the unknowns and defining appropriate conditions.
- Represent the unknown quantities using variables.
- Formulate an equation that expresses the relationship between the variables.
- Solve the equation to find the solutions.
- Verify the solutions by checking if they satisfy the conditions given in the problem statement.

## Problem-Solving Tips for Algebraic Equations

Let’s apply these steps to solve some specific math problems.

### Solving Problems from Page 58, 59, and 60 of the Mathematics Textbook

Today, we will solve problems from pages 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, and 53, as well as pages 58, 59, and 60 of the algebra textbook. The problems are all related to finding solutions using algebraic equations.

### Problem 41: Choosing Numbers to Satisfy Certain Conditions

In this problem, our friend Hùng asks Minh and Lan to choose numbers so that their difference is 5 and their product is 150. Let’s find out what numbers Minh and Lan should choose.

Solution:

To solve this problem, we can set up the following equation:

(x + 5) * x = 150

Where:

- x represents the number chosen by Minh
- (x + 5) represents the number chosen by Lan

By solving the equation, we find that Minh should choose the number 10 and Lan should choose the number 15.

### Problem 42: Calculating Interest Rate

In this problem, Bác Thời borrows 2,000,000 đồng from a bank for one year. However, he is allowed to extend the term for one more year. The interest from the first year is added to the capital for calculating the interest of the second year. If he has to repay a total of 2,420,000 đồng after two years, what is the interest rate?

Solution:

Let’s assume the interest rate is x (%), where x > 0.

The interest after one year is given by: 2,000,000 * x/100, which can be simplified to 20,000x.

After one year, the total amount Bác Thời has to repay is: 2,000,000 + 20,000x.

The interest for the second year is: (2,000,000 + 20,000x) * x/100, which can be simplified to 20,000x + 200x^2.

The total amount Bác Thời has to repay after two years is: 2,000,000 + 40,000x + 200x^2.

By setting up the equation 2,000,000 + 40,000x + 200x^2 = 2,420,000, we can solve for x.

After solving the equation, we find that the interest rate is 10%.

### Problem 43: Finding the Speed of a Boat

In this problem, a boat travels from Cà Mau to Đất Mũi along a river that is 120 km long. The boat stops for 1 hour at Năm Căn. On the return journey, the boat takes a longer route that is 5 km longer and travels 5 km/h slower than the speed on the forward journey. Determine the speed of the boat on the forward journey, given that the time taken for the return journey is the same as the forward journey.

Solution:

Let’s assume the speed of the boat on the forward journey is x km/h, where x > 0. The speed on the return journey is x – 5 km/h.

Since the boat stops for 1 hour, the total time taken for the forward journey is: 120/x + 1 hours.

The longer route for the return journey is: 120 + 5 = 125 km.

By setting up the equation (x + 5) * (x – 5) = 125x, we can solve for x.

After solving the equation, we find that the speed of the boat on the forward journey is 30 km/h.

### Problem 44: Finding a Number with Specific Properties

In this problem, we need to find a number such that half of it minus half of one equals one.

Solution:

Let’s assume the number we’re looking for is x.

The expression “half of it minus half of one” can be written as: (x/2 – 1/2).

By setting up the equation x^2 – x – 2 = 0, we can solve for x.

After solving the equation, we find that the number we’re looking for is either -1 or 2.

### Problem 45: Finding Two Consecutive Natural Numbers

In this problem, we need to find two consecutive natural numbers whose product is greater than their sum by 109.

Solution:

Let’s assume the smaller number is x, where x > 0. The next consecutive number is x + 1.

Their product is given by x(x + 1), which can be simplified to x^2 + x.

By setting up the equation x^2 + x – 2x – 1 = 109, we can solve for x.

After solving the equation, we find that the two numbers we’re looking for are 11 and 12.

### Problem 46: Finding the Dimensions of a Rectangular Piece of Land

In this problem, we need to find the dimensions of a rectangular piece of land with an area of 240 m². If the width is increased by 3 m and the length is decreased by 4 m, the area of the land remains the same.

Solution:

Let’s assume the width of the land is x m, where x > 0.

Since the area of the land is 240 m², the length is given by 240/x m.

If the width is increased by 3 m and the length is decreased by 4 m, the new width is x + 3 m and the new length is (240/x) – 4 m.

By setting up the equation (x + 3) * [(240/x) – 4] = 240, we can solve for x.

After solving the equation, we find that the width is 12 m and the length is 20 m.

### Problem 47: Finding the Speed of Two Cyclists

In this problem, we have two cyclists traveling from village A to village B, a distance of 30 km. The first cyclist’s speed is 3 km/h faster than the second cyclist’s speed. The first cyclist arrives half an hour earlier than the second cyclist. Let’s find the speed of each cyclist.

Solution:

Let’s assume the speed of the first cyclist is x km/h, where x > 3. The speed of the second cyclist is x – 3 km/h.

The time taken for the first cyclist to travel from A to B is 30/(x + 3) hours.

The time taken for the second cyclist to travel from A to B is 30/(x – 3) hours.

Since the first cyclist arrives half an hour earlier, we can set up the equation (30/(x + 3)) – (30/(x – 3)) = 0.5.

After solving the equation, we find that the speed of the first cyclist is 15 km/h and the speed of the second cyclist is 12 km/h.

### Problem 48: Finding the Dimensions of a Metal Sheet

In this problem, we need to divide a metal sheet into four squares at the corners, each with a side length of 5 dm, to make a rectangular box without a lid. The volume of the box is 1500 dm³. Let’s find the dimensions of the original metal sheet, assuming the length is twice the width.

Solution:

Let’s assume the width of the metal sheet is x dm, where x > 0.

The length of the metal sheet is 2x dm.

When the sides are folded to form a box without a lid, the length becomes 2x – 10 dm, the width becomes x – 10 dm, and the height becomes 5 dm.

The volume of the box is given by 5(2x – 10)(x – 10) dm³.

By setting up the equation 5(2x – 10)(x – 10) = 1500, we can solve for x.

After solving the equation, we find that the width of the metal sheet is 20 dm and the length is 40 dm.

### Problem 49: Finding the Time Required for Two Teams to Complete a Task

In this problem, two teams are working together to complete a task in 4 days. If they work separately, Team I completes the task 6 days earlier than Team II. Let’s find out how many days each team takes to complete the task individually.

Solution:

Let’s assume Team I takes x days to complete the task individually, where x > 0.

The time taken by Team II to complete the task individually is x + 6 days.

The amount of work done by Team I in one day is 1/x, and the amount of work done by Team II in one day is 1/(x + 6).

By setting up the equation (1/x + 1/(x + 6)) * 4 = 1, we can solve for x.

After solving the equation, we find that Team I takes 6 days to complete the task individually, and Team II takes 12 days.

### Problem 50: Finding the Density of Two Metal Pieces

In this problem, we have two metal pieces, one weighing 880 g and the other weighing 858 g. The volume of the first piece is 10 cm³ less than the volume of the second piece, and the density of the first piece is 1 g/cm³ greater than the density of the second piece. Let’s find the densities of the two metal pieces.

Solution:

Let’s assume the density of the first metal piece is x g/cm³.

The density of the second metal piece is x – 1 g/cm³.

The volume of the first piece is 880/x cm³.

The volume of the second piece is 858/(x – 1) cm³.

By setting up the equation 880/x – 858/(x – 1) = 10, we can solve for x.

After solving the equation, we find that the density of the first metal piece is 8.8 g/cm³ and the density of the second metal piece is 7.8 g/cm³.

### Problem 51: Finding the Amount of Water in a Solution

In this problem, we add 200 g of water to a solution containing 40 g of salt. The concentration of the solution decreases by 10%. Let’s find the amount of water in the solution before adding more water.

Solution:

Let’s assume the amount of water in the solution before adding more water is x g, where x > 0.

The concentration of salt in the solution before adding water is 40 / (x + 40).

After adding 200 g of water, the total weight of the solution becomes x + 40 + 200 g.

The concentration of salt in the solution after adding water is 40 / (x + 240).

By setting up the equation (x + 40)(x + 240) = 400(x + 240 – x – 40), we can solve for x.

After solving the equation, we find that the amount of water in the solution before adding more water is 160 g.

### Problem 52: Finding the Speed of a Canoe

In this problem, a canoe travels from point A to point B, with a distance of 30 km. It rests for 40 minutes at point B before returning to point A. The total time taken for the entire journey is 6 hours. Let’s find the speed of the canoe in calm water, given that the speed of the current is 3 km/h.

Solution:

Let’s assume the actual speed of the canoe is x km/h, where x > 3.

The speed of the canoe when traveling downstream is x + 3 km/h.

The speed of the canoe when traveling upstream is x – 3 km/h.

The time taken to travel downstream is 30 / (x + 3) hours.

The time taken to travel upstream is 30 / (x – 3) hours.

Since the time taken for the return journey is the same, we can set up the equation (30 / (x + 3)) – (30 / (x – 3)) = 0.5.

After solving the equation, we find that the speed of the canoe in calm water is 12 km/h.

### Problem 53: The Golden Ratio

In this problem, we need to divide line AB in a certain ratio so that the ratio of the longer segment to the entire line is equal to the ratio of the shorter segment to the longer segment. This ratio is known as the golden ratio.

Solution:

Let’s assume M is the point that divides line AB, and AM is greater than MB. Let’s find the golden ratio.

Solution:

Let’s assume M is the point that divides line AB, and AB has a length of a.

Let AM = x (0 < x < a). In that case, MB = a – x.

We can set up the equation (x / a) = ((a – x) / x).

After solving the equation, we find that the golden ratio is approximately 1.618.

In conclusion, using algebraic equations, we can solve a variety of math problems. By following the steps outlined in this article, you’ll be well-equipped to tackle problems of your own. Happy problem-solving!

**For more math problem-solving tips and techniques, check out the website Kienthucykhoa.com.**