Grade 7Mathematics

Algebra Basics

Variables, simple equations, substitution.

📖 6 min read · 4 worked examples · 7 practice questions

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The lesson

Habari zenu students! Don't let the big word scare you—Algebra is just a clever way of solving puzzles we meet every day here in Kenya, like at the market or on the farm. What is it exactly? In Algebra, we use letters to stand for numbers we don't know yet. We call these letters 'variables' because their value can change or vary. Let's use an example you all know. Imagine you have a bag of mangoes, but you haven't counted them yet. Instead of guessing, we just call that mystery number 'x'. If you go to the kiosk and buy 2 more mangoes, how many do you have? Since we started with 'x' and added 2, we write it simply as x + 2. See? You're already doing Algebra! You might wonder, why bother with letters? We use them to solve problems when the numbers are missing, or to describe rules that work for any amount. It makes us real math detectives.

Habari zenu class! You know, in math, we often see many numbers and letters, but they aren't all doing the same job. It's like the difference between a phrase and a full sentence in English. First, let's look at an Expression. Think of it as a mathematical 'phrase'. It tells us something, but it doesn't give us a final answer or a balance. See this example here: 3y + 5. It has numbers and a letter, but importantly, there is no equal sign! It's like saying 'three mangoes and five more' without saying how many they total to. At an Equation. This is like a complete sentence. It tells us that two things are exactly the same. The secret weapon here is the 'equal sign'. At x + 4 = 10. This tells us a full story: some number plus four gives us exactly ten. Whenever you see that '=' sign, you know you are dealing with an Equation! To really master this, we need to know the names of the parts. Let's break down these pieces so we don't get confused when we start solving them. The 'Variable' is just a letter, like 'x' or 'y'. It's a placeholder for a number we don't know yet—like a hidden prize in a box. The 'Coefficient' is the number that is stuck to the letter, like the 3 in 3y. It tells us how many of that variable we have. The 'Constant'? That's just a plain number standing on its own, like the 5 or the 10. It never changes, it stays constant! Do we all see the difference now between a phrase and a full mathematical sentence?

Done, class! Let's look back at the big ideas we've covered in our journey through the foundations of algebra. You've all worked very hard! First, we talked about variables. Remember, these are just letters like 'x' or 'y' that stand in for numbers we don't know yet—like a hidden treasure in a box. Second, we learned about balance. Think of the equals sign like a weighing scale at the market. Whatever you do to the left side, you must also do to the right side to keep it level. Then, we mastered inverse operations. This is our secret tool for solving equations! If you see addition, you use subtraction to undo it. If you see multiplication, you use division. It's all about doing the opposite. Looking ahead, our next step will be learning how to group 'like terms' together to simplify even bigger problems. It's going to be like sorting different types of fruits into their own baskets. Asante sana! You are all becoming great mathematicians. Before we close, does anyone have a final thought on how balance helps us in real life or in math?

Worked examples

Substitution: Worked Example 1

We call it 'Substitution'. Think of it like a football match—when one player comes off the pitch and another takes their place. In mathematics, substitution means we take a letter, which we call a variable, and we replace it with a specific number. It's like putting a value into a placeholder. We want to find the value of this expression: '3p plus 2'. Wait, we need to know what 'p' represents first. The problem tells us that p is equal to 5. Everywhere we see a 'p', we are going to put 5 instead. Step 1 is simple: Replace 'p' with 5. It becomes 3 times 5, plus 2. Brackets help us keep things tidy so we don't get confused. Step 2, we follow our BOMDAS rules. First we multiply 3 by 5 to get 15. Then we add the 2. 15 plus 2 gives us 17. That is our final answer! Always remember, when you see a number and a letter together like '3p', it means they are multiplying. Don't just write 35! Use brackets to show it's 3 times 5.

Solving 1-Step Equations: Worked Example 2

Habari zenu class! Moving on with our equations, let's look at another worked example to make sure we are all together. We are going to solve this one step by step, just like we are following a recipe for ugali. Remember our big goal: we want to leave the variable 'x' all alone on one side. It is like trying to give 'x' its own seat in a crowded matatu. Here is our equation: x minus 7 equals 15. You see that minus 7? It is bothering our x, so we need to move it. To remove a minus, we do the opposite. What is the opposite of taking away? It is adding! We add 7 to both sides of the equals sign to keep the balance. Minus 7 and plus 7 become zero, they cancel out! On the other side, 15 plus 7 gives us our answer. There we have it, x equals 22. Simple, right? Always remember to treat both sides of the equation the same way, like fair juice sharing. Before we try the next one, just keep this memory aid in your head: use inverse operations to undo what is happening to the variable. If you see subtraction, you use addition.

Solving 2-Step Equations: Worked Example 3

Jambo everyone! We are going to look at a more challenging example. Don't worry, we'll take it step by step just like we do when we're peeling a banana. At our equation here: 2x plus 3 equals 11. Our job is to find the value of x, but it's hidden behind the 2 and the 3. In Step 1, we start with the number that is furthest from x. That's the 3. Since it is added, we undo it by subtracting 3 from both sides. It's like taking away three mangoes from two balanced baskets. When we subtract 3 from 11, we are left with 8. We have a simpler problem: 2x equals 8. Step 2 is to undo the multiplication. Since 2 is sticking to the x, we divide both sides by 2. 8 divide by 2 gives us 4. X equals 4. We have solved it. Never forget the Golden Rule: Always undo the addition or subtraction before you touch the multiplication or division. It's like taking off your shoes before your socks!

s in Daily Context

Jambo everyone! Today we are moving from words to math. Ever wondered how your daily life can be written as an equation? Imagine a matatu starts with 'y' passengers. We don't know the number, so we use a letter. The story says 5 passengers alight—that means they get off. If 10 people are left inside, how do we write that? We write y minus 5 equals 10. Alighting is a subtraction. See how simple that translation is? Next, let's look at Scenario 2. If you buy 3 textbooks and the total is 450 Shillings, we let 'b' represent the price of one book. When we have 3 books, we multiply. 3 times b, or just 3b, equals 450. We can solve for the price of just one book! To help you out, here is your secret math dictionary. When you hear 'more than', think plus. When you hear 'alight' or 'less than', think minus. Remember, 'is' or 'total' always translates to our equals sign. 'Per' or 'each' usually signals multiplication or division.

Practice questions

  • For our first question, imagine you have some mangoes in a basket—we'll call that amount 'a'. If I give you 12 more and you end up with 20, how many did you start with?
  • In the second one, we have 5m = 25. In math, when a number and a letter sit tight together like that, it means they are multiplying.
  • Take a moment to write down your steps. Don't just guess the answer—show us how you moved the numbers across the equals sign.
  • For our first question, we have a puzzle: 3x minus 4 equals 14. Remember our rule—we want to get 'x' by itself.
  • At the second one. This is a real village story!
  • I can see some of you thinking hard—that's the spirit! Remember, in algebra, whatever you do to the left side, you MUST do to the right side to keep the balance, just like a weighing scale at the market.
  • You've shown that you can handle these two-step equations with confidence. Before we finish this session, let's think about how these equations help us in real life, especially when we are planning or shopping.

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