Hey there! I am Studyfin, your math guide. Today, we will learn how to find missing numbers using simple balance tricks!
In pre-algebra, we use a letter like 'x' to stand for a mystery number. This letter is called a variable because its value can change depending on the puzzle.
To solve a mystery, think of an equation like a balanced playground scale. Whatever you do to one side, you must do to the other side to keep it perfectly level.
To find our mystery number, we do the opposite math action. If the puzzle adds a number, we subtract it from both sides to get our variable all by itself.
✏️ Worked example
Solve the mystery equation for x: x + 5 = 12
Look at the equation: x + 5 = 12. Our goal is to get the variable 'x' completely by itself on the left side.
Identify the operation happening to x. Here, 5 is being added to x.
Perform the opposite operation. The opposite of adding 5 is subtracting 5.
Subtract 5 from both sides of the equal sign to keep the scale balanced: (x + 5) - 5 = 12 - 5.
Simplify both sides. On the left, 5 - 5 becomes 0, leaving just x. On the right, 12 - 5 becomes 7.
Write your final answer: x = 7. You solved the mystery!
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