Algebra rules
Remember in the second grade when your teacher
asked you to fill in the box in a problem like this: | 4 + ⬜ = 10 |
In algebra all we do is use a letter, like "X" instead of a box: | 4 + X = 10 |
This equation asks you: What number equals 10 when you add 4 to it?
The answer to this question is 6, because 4 + 6 = 10.
Here are some simple equations:
| Equation | The
question it asks | The answer | Reason |
| X + 5 = 15 |
If you add 5 to my number you get 15. What is my number? |
X = 10 |
Because 10 + 5 = 15 |
| X - 13 = 13 |
If you subtract 13 from my number you get 13. What is my number? |
X = 26 |
Because 26 - 13 = 13 |
| 3X = 18 |
If you multiply my number by 3, you get 18. What is my number? |
X = 6 |
Because 3 times 6 = 18 |
| X/4 = 5 |
If you divide my number by 4, you get 5. What is my number? |
X = 20 |
Because 20/4 = 5 |
How about something more complex, like this equation: 2X - 5 = 11
Here's how you solve an equation of this type:
| 1. Cover up the "2X" with your finger (I'll use a box): | ⬜ - 5 = 11 |
| 2. Now solve for the value of the "box": |
⬜ = 16 because 16 - 5 = 11 |
| 3. Now look at what is in the ⬜ : |
2X = ⬜ = 16 |
| 4. Now solve the above easy equation: |
X = 8, because 8 times 2 = 16 |
Here are some other equations, and how you would solve them:
| Equation |
Step 1: Cover up the term with X in it |
Step 2: Solve for the boxed term |
Step 3: Look at what's in the box and solve for it |
| 3X + 1 = 7 |
⬜ + 1 = 7 |
⬜ = 6
because 6 + 1 = 7 |
3 X = the ⬜ which is 6,
so X = 2, because 3 X 2 = 6 |
| X/2 - 1 = 3 |
⬜ - 1 = 3 |
⬜ = 4
because 4 - 1 = 3 |
X/2 = the ⬜ which is 4,
so X = 8, because 8/2 = 4 |
Now, here's a problem for you: 4 X + 7 = 19 X = _______
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