Objectives (5 - 7 minutes)

1. Understanding the concept of simple interest: The teacher must ensure that students understand what simple interest is, how it is calculated, and how it can be applied in everyday situations.

2. Knowing how to apply the formula for simple interest: Students should be able to apply the formula for simple interest to solve problems involving the calculation of interest, principal, rate, and time.

3. Solving practical problems involving simple interest: After acquiring the theoretical knowledge, students should be able to solve practical problems involving the calculation of simple interest, demonstrating the application of the learned concept.

Secondary Objectives

• Stimulating critical and analytical thinking: In addition to learning the formula and how to apply it, it is important for students to develop critical and analytical thinking skills to understand the logic behind the calculation of simple interest.

• Promoting interaction and teamwork: During the lesson development, the teacher should encourage active participation from students, promoting interaction and teamwork for problem-solving.

Introduction (10 - 15 minutes)

1. Review of previous concepts: The teacher should start the lesson by reviewing the basic concepts of percentage and proportions, as they are fundamental for understanding simple interest. A quick review can be done by proposing some simple problems for students to solve in groups. (3 - 5 minutes)

2. Problem situations: Next, the teacher should present two problem situations that illustrate the importance and applicability of simple interest. For example:

   • Situation 1: 'Imagine you lent $100.00 to a friend and established that he should pay you $5.00 in interest each month. How could you calculate the total amount he would have to pay you after 6 months?'

   • Situation 2: 'If you invested $1,000.00 in a financial application that yields 0.5% per month, how much would you have after 1 year?'

   The teacher should emphasize that, although the situations may seem simple, they involve the calculation of simple interest, a fundamental mathematical concept in finance and economics. (5 - 7 minutes)

3. Contextualization: The teacher should contextualize the importance of simple interest, explaining that it is present in various everyday situations, such as bank loans, vehicle and real estate financing, and even in financial investments. Understanding and being able to calculate simple interest can help students make more informed financial decisions and avoid unnecessary debts. (2 - 3 minutes)

4. Introduction to the topic: To spark students' interest in the topic, the teacher should present some curiosities and practical applications of simple interest. For example:

   • 'Did you know that the notion of simple interest is as old as civilization itself? The ancient Babylonians, who lived over 4,000 years ago, already used the concept of simple interest in their commercial transactions!'

   • 'How about this curiosity? Have you heard of the famous chess game called 'Wheat and Chessboard'? In this game, players place grains of wheat on a chessboard, doubling the quantity on each new square. The total grains at the end of the game are a practical example of how simple interest can accumulate rapidly!'

   After these curiosities, the teacher should formally introduce the topic, explaining that simple interest is a powerful mathematical tool for calculating the cost or gain of time in financial transactions. (3 - 5 minutes)

Development (20 - 25 minutes)

1. Theory - Simple Interest (10 - 12 minutes): The teacher should start the theoretical part of the lesson by explaining the concept of simple interest. It should be emphasized that simple interest is calculated only on the initial capital amount, without considering the interest accumulated in previous periods. The teacher can use the example of the loan to a friend mentioned in the Introduction to illustrate the concept.

   • The teacher can begin by explaining the formula for simple interest: I = P * r * t, where I is the interest amount, P is the principal, r is the interest rate, and t is the time the principal is invested.

   • Next, each element of the formula should be explained. For example, the interest rate should be expressed in decimal or percentage form, and the time should be expressed in the same time unit as the interest rate.

   • The teacher should explain that the formula for simple interest can be rearranged to find any of the four variables. For example, if the student knows the principal, the interest rate, and the time, they can use the formula to calculate the interest.

   • The teacher should also mention that the formula for simple interest can be used to calculate the principal, the interest rate, or the time, if the other three variables are known.

2. Practical examples of applying the formula (5 - 7 minutes): After the theoretical explanation, the teacher should present some practical examples of how to apply the formula for simple interest to solve problems.

   • The teacher can start with simple examples, such as the loan to the friend mentioned in the Introduction, and then move on to more complex examples, such as the investment in the financial application.

   • For each example, the teacher should explain step by step how to solve the problem, calculating the interest, principal, interest rate, or time, as the case may be.

   • The teacher should also emphasize the importance of paying attention to time units and expressing the interest rate consistently with the chosen time unit.

3. Practical activity - Problem-solving in groups (5 - 6 minutes): After presenting the examples, the teacher should divide the class into groups and give each group some problem situations to solve. The problem situations should involve the calculation of simple interest and require the application of the formula.

   • The teacher should circulate around the room, assisting groups that have difficulties and ensuring that all students are participating actively.

   • At the end of the activity, the teacher should ask a representative from each group to present the solution to one of the problem situations to the class, explaining step by step how they arrived at the answer.

   • The teacher should correct the solutions presented by the students, highlighting the positive points and pointing out possible errors, in order to promote learning and understanding of the concept of simple interest.

Feedback (8 - 10 minutes)

1. Group discussion (3 - 4 minutes): The teacher should gather all students and promote a group discussion about the solutions presented. At this stage, the teacher should ask questions to encourage students to reflect on what they have learned and to connect the acquired knowledge with everyday situations. Some questions that can be asked are:

   • 'How did you arrive at the solution to this problem?'
   • 'Can you see how the concept of simple interest applies to everyday situations?'
   • 'What were the biggest difficulties encountered in solving these problems?'

2. Learning verification (2 - 3 minutes): The teacher should then verify what the students have learned, asking them to explain in their own words the concept of simple interest and how to apply the formula to solve problems. The teacher can ask questions like:

   • 'What are simple interests and how are they calculated?'
   • 'What is the formula for simple interest and how can it be used to solve problems?'
   • 'Can you think of other everyday situations that involve the calculation of simple interest?'

3. Final reflection (3 - 4 minutes): Finally, the teacher should propose that students reflect for a minute on the following questions:

   • 'What was the most important concept you learned today?'
   • 'What questions have not been answered yet?'

   The teacher should then ask some students to share their answers with the class. This final reflection activity helps consolidate learning and identify any gaps in students' understanding that can be addressed in future lessons.

4. Conclusion: The teacher should conclude the lesson by emphasizing the importance of the concept of simple interest for everyday life and for making financial decisions. It should be emphasized that with the understanding and ability to calculate simple interest, students will be better prepared to deal with financial situations and make informed decisions about loans, investments, and personal financial planning.

Conclusion (5 - 7 minutes)

1. Summary of Contents (2 - 3 minutes): The teacher should start the Conclusion by giving a brief summary of the main points covered during the lesson. The concept of simple interest, the formula for calculating interest, the importance of expressing the interest rate consistently with the chosen time unit, and how to apply the formula to solve problems should be recapitulated. The teacher can do this interactively by asking students to complete sentences or answer brief questions.

2. Connection between Theory and Practice (1 - 2 minutes): Next, the teacher should explain how the lesson connected theory (the concept of simple interest and the formula for its calculation) with practice (problem-solving and discussion of everyday situations involving the calculation of simple interest). The teacher can emphasize that understanding the concept and the formula is essential for effectively solving problems and applying knowledge in real situations.

3. Additional Materials (1 - 2 minutes): The teacher should then suggest some additional materials for students who wish to deepen their understanding of the topic. This may include financial mathematics books, educational websites with videos and interactive tutorials, and additional exercises to practice calculating simple interest. The teacher can also encourage students to look for examples of simple interest in their daily lives, such as in bank and financial advertisements, to reinforce the importance and applicability of the concept.

4. Importance of the Topic (1 minute): Finally, the teacher should emphasize the importance of the topic for everyday life and for students' education. It should be explained that the ability to calculate simple interest and understand how it works is essential for making informed financial decisions, such as choosing between different loan or investment options. Additionally, the teacher can highlight that knowledge of financial mathematics, including the calculation of simple interest, is a valued skill in the job market, especially in areas such as finance, accounting, and administration.